dtgreene: I'm not actually familiar with that game.
LootHunter: Are you sure? It's actually called
Darkest Dungeon (there is no "The", my mistake). And it's a very well-known game.
In that game you hire party members between the raids into the dungeons. They don't have detailed backstory but they do have random qualities (quirks), some of which you can remove or add through special means, like visit to Sanitarium.
That game should fall in between the two styles mentioned by the OP. But me personally, I think I would prefer for the game (Darkest Dungeon) to lean more to the second category, since a huge part of the characters can eventually be customized (for example, despite the fact that different characters of the same class would have different opening sets of skills, you can eventually unlock the other skills as you gain more gold), and for the characters' backgrounds, you can more or less use your imagination on how some of the characters got themselves there in the first place. Although there are comic strips explaining the backgrounds of the characters, it'd be kind of dull to think that all the characters of the same class come from the same origin. What I mean is, you can apply the official background to the first new character you get, and use your imagination for the next characters of the same class.
As for the OP's question, I'd say both. If anything, it'd be nice if you can customize your main character and have the other characters premade, since creating one character often already takes too much from me, and having to repeat the same process for the other characters would be too time-consuming.