Vila has been described as a social delinquent, but to me he has a lot of integrity and honesty (despite being a thief), and the most humanity of the regulars in the series.
Fearful but brave
First of all, my definition of bravery is the ability to act despite fear. If people are not afraid in the first place, in my opinion they're not brave—they're fearless.
Vila has a lot of fears—e.g. darkness, claustrophobia, blood, and violence—especially personal. But he can conquer them if he tries, and almost always operates well under fire (e.g. on the neutron blasters, picking locks), often while making jokes and wisecracks. He can get very frightened though if he has nothing to do and time to think, particularly if he's alone. He was terrified by Travis on Exbar (personal violence) and panicked badly afterwards in the storage room after being kicked by Avon (claustrophobia and violence).
He is brave when he's mentally occupied or can use his skills. He can be very brave to help others, e.g. pulling his gun on Kayn to help Gan; staying by the life pods to wait for the crew after the Andromedan war when he could have left; conquering his claustrophobia, fear of the dark and loneliness to set up Avon's Anna cave; rescuing Tarrant on Terminal and trying to rescue Cally; his 'one-man rescue mission' in 'Games'.
His ethics
Vila almost always objects to violence and murder, (even of the supposed assassin Cancer). His ethics are individual—he considers it immoral of Avon to consider a deal with the London crew (and even suggests killing him in self-defence though he wouldn't do it himself), but crookedness per se is OK. In other words, crimes against property are acceptable, but not against people, especially him. He retains his ethics and personal standards (even if they're not as high as Gan's or Cally's) throughout the series despite some physical and a lot of verbal abuse from fellow crew members. He describes himself fairly accurately as harmless; he rarely harms anyone intentionally, certainly never a friend or ally. He never pays anyone back for bad treatment (e.g. abuse from Dayna, Tarrant and Avon), though this could be due to fear of retribution.
He has no qualms about operating the weapons console on Liberator however, and cheers when he scores a hit. It's impersonal; he doesn't see the results. He can delude himself that it's not the same as killing someone face-to-face.
Honesty
Vila is very honest about himself, possibly because he would be a bad liar anyway, with that expressive face which shows everything he feels. He's completely open about being afraid, lazy, and a thief.
Kind-hearted
Vila says he is pleased that Cally is back after her capture and torture by Travis, and forces Avon to say so too. He often offers drinks and comfort to crew members who are shaken or hurt, notably Avon in 'Rumours of Death', and is usually the one to ask after anyone who has been hurt. He was even concerned for the unconscious Dorian, trying to make him comfortable in a Scorpio flight chair. And it's always Vila who tries to cheer others up with jokes, drink, or food. :-)
Trust
Vila trusts and likes Blake which is why he stays with him, though he considers leaving after Gan's death; he loses a lot of his trust at that point. He also mostly trusts Avon until Malodar, and certainly also trusted Gan, Jenna and Cally. He consistently mistrusts Tarrant with some reason.
He loses his trust of all of them when no one stands up for him against Tarrant in 'City', but was probably reassured by his welcome back—for a while anyway.
He is also fairly trustworthy in the big things (but not what he thinks of as the small things—staying alert and awake on watch and teleport duty). He is the only person Avon trusts after Cally dies though he doesn't say so—Vila is the only one Avon ever deliberately leaves in sole charge of Scorpio ('Cancer' and 'Gold'), and is even trusted to go off in it and return to pick the others up ('Gold').
Resilient and cheerful
Vila bounces back from being terrified or emotionally hurt very quickly in the first three seasons; he's extraordinarily resilient. People insult him or ignore him, and he is usually only briefly hurt (watch his face) but comes back cheerfully for more, like a puppy: eager and still hoping to be liked.
In season 4, the systematic denigration (dare I say vilification?) and contempt from the others, and the absence of Cally's companionship, demoralise him so much that he loses much of this resilience, is driven to drink, and rarely smiles.
A brilliant thief but not a compulsive one
Although Vila has been a thief from early youth, he hardly ever steals n the series, and never on his own account (with the exception of Blake's watch, and given his later brilliance, that must have been a ploy—see below). The only theft I can think of off-hand is the 'Feldon crystal' necklace. If he'd been a compulsive thief, he'd have robbed the crew blind, and everyone else encountered, despite the consequences. I imagine he was branded compulsive because he couldn't be conditioned—the Federation bureaucracy stuck him in a handy box because he didn't fit their usual categories.
He seems to get his kicks from demonstrating his cleverness in picking locks regardless of any profit. It's certainly the only thing he's proud of about himself. Perhaps he's a compulsive picker of locks rather than a compulsive thief as such. He loves the challenge, and it's probably the only thing that was ever valued about him.
Taking Blake's watch and going for his wallet was so clumsy and out of character, especially for the skilled master thief he is, I think he did it deliberately in Jenna's sight to look foolish and inept, and therefore no threat to any of the tough characters in the holding cells.
Witty
Wit is obviously his second-greatest talent, and he's brilliant at it, even when very nervous and under fire.
Intelligent
The sarcophagus alien says he is a genius pretending to be an imbecile, and later that he has an unusually sharp intelligence. Despite what must have been a rudimentary education, probably not much beyond primary level (given he was in the juvenile detention wards before being shipped to a penal colony at age 14) he has an excellent vocabulary, and learns very fast. He already has detailed technical knowledge related to locks (which would include computers, electronics, magnetic and force fields etc) when he joins the crew, and picks up other skills quickly—the neutron blasters, maintenance, the teleport, even some piloting, and other technical tasks on the Liberator.
He's good enough at chess and the pyramid game for Avon to enjoy playing him.
Although he asks some stupid questions at times (possibly through lack of attention to what has gone before) he can be very astute, as in 'Volcano'.
I think he learned very early not to show his intelligence to his fellow Deltas, in sheer self-defence. Being a clever thief however obviously had some social cachet as he never conceals that; indeed he's very proud of it.
He's largely self-educated, but does seem to have a lot of knowledge one wouldn't normally expect from him—e.g. how freighters are pressurised in flight, how to fix a hull breach with a local force field.
I think he's well-read too, because of his vocabulary and his love of a good story.
Irresponsible
Yes, Vila is irresponsible, and I can understand why. In the criminal world, prison, and penal colonies, responsibility for an action or idea which went wrong would have dire, possibly fatal, consequences. He'd prefer to be a 'technical advisor', or just stay on the fringes. In 'Stardrive', he uncharacteristically makes a suggestion: using a meteorite to disguise their approach, then decides it will go wrong, which it does. His next suggestion is very indirect—a 'drunken' spiel about how to fix the damage without involving him.
Immature
He often seems to act like a big kid—"Ooh, I like stories!"—and shows a quite endearing innocence at times, which I'm amazed he ever retained after imprisonment as little more than a child. His 'passes' at women are so inept, they look like those of an inexperienced adolescent. He grows up a lot in season 4, but I'm not sure it's a change for the better, as he also loses his bouncy cheeriness and becomes bitter, depressed, and withdrawn.
Lazy
Hey, so am I! People say it like it's a bad thing!
Hypochondriac?
In the first two seasons, Vila often complains of aches, pains, illnesses etc. He seems to suffer more than others after being thrown about the flight deck. He's humorous when he complains about it, but I think he's really unwell. If he'd just been through another attempt at conditioning before being deported to Cygnus Alpha, he would have been affected physically, and the nerve damage heals gradually. Blake never sneers at him for it (perhaps he understands) and though Avon does sneer and joke about it, he seems concerned for Vila before he comes round in 'Dawn of the Gods'. I suggest nerve damage, as it could give him his 'pins and needles' when very stressed (e.g. on Exbar, when Avon and Blake accept this as quite a valid excuse and tell Inga to look after him). It also ties in with what he imagines they're doing to Tarrant in 'Traitor' (threading red hot filaments through his nerve centres).
I'm not sure I count the various excuses Vila tries to use to get out of dangerous missions ("I've got a weak chest") as I don't think he expects those to be believed.
Class
Vila says he comes from the Delta service grades and I see no reason to doubt that. His accent isn't as upper-class as the others, he uses more contractions in speech and small grammatical errors like 'me' instead of 'my'. He says he 'chose the wrong parents' and bought his grade 4 ignorance rating. From this I'd say he was born a Delta, tested as a higher grade, didn't fancy the hard work and possible danger involved, and bought a low rating as opposed to grade) so he could live in indolence, obscurity and safety. I do not see the 'ignorance rating' as synonymous with his Delta grade. I think people were rated within their grades.
I think a lot of the contempt (but not all) the others hold him in is due to his class. No matter how clever Vila is, he can never be an equal to most of them, rather like a southern US black before the 60s. Note who treats him the best. Blake, who is a revolutionary opposed to the repressive Federation system, treats him as well as he treats other crew members (no wonder Vila likes him). Cally who is an alien from outside the Federation, likes Vila and sympathises with him at times, though she too loses patience with him. Gan, a lower grade than the others, and traditionally from another planet, is his only overt friend. Soolin, also an outsider, seems to accept him well enough after her bad first impression of him. Avon likes Vila too, at least until season 4, but conceals it, though this could be due to Avon's dislike to revealing weakness as much as Vila's social standing. Oddly enough I don't think it even occurs to Vila that class prejudice might be a factor, perhaps because he was 'self-employed' on Earth.
Wine and women
Vila enjoys his drink, either adrenaline and soma or wine, but he doesn't need it as an addict or alcoholic would, at least not in the first three seasons. He goes quite long stretches without it, and he is rarely seen actually drunk. He drinks a lot on season 4 (understandably—he's quite badly treated and driven to it) but only appears the worse for wear a couple of times.
Vila often talks about women, and about pleasure planets etc, but I think this is just that—all talk, partially to amuse others, maybe also partially to say "Hey, I'm an adult male" to those who treat him as at best an adolescent. His laughable 'passes' at Dayna and Soolin are attempts to lighten the mood and relieve tension. I think he'd be quite unnerved if one of them took him up on an offer! Note that Kerril makes the first move. I don't think he's the hedonist some make him out to be; see his goals. I think Vila miscalculates when he tries to be the man of the world with this lot; what might have enabled him to fit in with his fellow Deltas doesn't impress the crew.
Goals
We hear what Vila really wants in life only a couple of times—safety, security, a family (swimming in the moonlight with his children). Poor guy. The other over-the-top stuff like the palace with the diamond floors and the virgins in red fur is only to amuse—in this particular case, an almost manic Avon on the Malodar shuttle who appears to be friends again with Vila.
Vila doesn't want revenge or power or some high unattainable ideal like the others. He really isn't cut out to be a rebel. He just wants happiness, security and love, and the chance to show his lock-picking talents off.
But he'd settle for a friend, and sadly he doesn't even have that after Gan dies.