Who's backstory would you like to know the most about?
1) Mal: How did he end up fighting as a browncoat?
2) Zoe: Same as Mal, How did he really earn her loyalty? Was it over years or was there one defining event?
3) Wash: Why did he become a pilot? If he was so good, why did he end up on Serenity?
4) Book: How did he end up as a Shepard and what was he before?
5) River/Simon: Is there anything else we need to know?
6) Jayne: I don't know if there are any questions, but there has got to be some good stories.
7) Kaylee: We got a little of her backstory, but is there something we don't know?
Inara: What was a companion of her quality really doing out there "in the black"?
Since BSG is entering its last season, I wonder if someone could get SciFi to make more of Firefly. I doubt it, but I have a better chance of that than I do of finding the "Impossible Dreams" video store.
Book. Hands down. I think I have his history pegged, and I'd really like to see if I'm right, what his former life was like, and how he came to be what he is.
First runner up is Badger: totally overlooked, but probably one of the most interesting characters on the show.
In no particular order:
Mal: I'd like to know what his beef is with the alliance because it's SO personal. I'd guess it was either multiple events (systematic destruction of all the towns on his planet) or some act of unusual cruelty (burning his mother's new caravan, with her in it).
Jayne: To see his family life, where he came from, and why he's so damn good at fighting.
Inra: How she became a companion, space-hooker boot camp, and why she's so eager to be on the Alliance's fringes.
The Tams: To get a better view of life in Alliance space.
Other:
Zoe: Not so terribly interested in her back story, but she makes a great straight-man for the whole crew. I'd like to see the "Secret Life of Zoe." the one where she dreams of becoming, I dunno, a mime, or a ballet dancer. Something totally incongruent.
Wash: Again, not terribly interested in his back story, but I would like to see inside his head. A whole episode of dino-therapy.