I'm not planning to run a campaign, but I had often thought of how nicely the game would map to d20 Modern.
I'm curious as to the Star Wars classes for people.
For d20, I'd go with (and this is off the top of my head)
Zoe: Fast/Gunslinger -- easy. She's probably smart/wise, but she hasn't shown any real other major characteristics. She's a heck of a shot, though. Estimated level: 11.
Wash (Note: Far, far away from books). What's the Drive skill again? Int or Dex? He'd pretty much be a mid-level Smart hero with all kinds of ranks in Pilot and Navigate. Estimated level: 7 (in the pilot, Mal has to give him suggestions on what to do -- but he IS good).
Inara -- Dedicated/Charismatic/Personality, possibly with a few levels of Negotiator. At the very least, she needs a BIT of Dedicated ability to be as empathic and able to read people as a Companion should be. Estimated level: 12.
Jayne -- Strong/Tough/Soldier. He ain't fast and he ain't smart and he ain't pretty. But darn, can he kill things effectively. Estimated level: 11.
Kaylee -- Smart/Field Scientist. Estimated level: 6, with maxed out Craft ranks as appropriate.
Book -- not a clue. Obviously he's got some Dedicated going on in there, but Joss Whedon dropped enough hints that, like any preacher in a western, the guy has a dark and violent past. My guess would be Strong/Dedicated/Soldier, and if you had an Advanced class for a preacher-type, you could stick it in there -- maybe a Negotiator with different flavor text? Estimated level: Probably 12 or 13 total, though he's not using his soldier abilities anymore, so maybe he's atrophied to level 11 or so.
Simon -- Smart/Field Medic. A non-optimized path, but he really is more intelligent than he is Wise (although I'd argue that for a TV show to be fun, everyone has to be a bit less Wise, so that they fall for the bad guy's plot for the first forty-five minutes). Give him the Medical profession and he'll have the necessary skills. Estimated level: 5
River -- Smart/Telepath. Estimated level: 5? 7? She
Mal -- the toughie. He's a great shot, he negotiates decently well, he can fight like a fury, though he's apt to get his butt handed to him if caught by surprise. I'd go with (strong?)Tough/Dedicated/Soldier/Negotiator. He's got the early tough (and maybe Strong) stuff from his soldiering days, where he picked up Knowledge(tactics) and such. I'd give him one level of Tough because of his ability to fix a ship while bleeding to death. As a leader, he seems to use his Dedicated skills a fair amount, and now that he's living the life of crime, he's picked up some ranks in Bluff by going the Negotiator route. Estimated level: 13. High enough to be influential and get his stuff done, and high enough so that if he'd really focused on one thing, he would have been great at it. But he's got a lot of classes floating around there, and he's a Jack of all Trades.
Not crazy enough to try and put individual feats and talents in there. But those would be my votes, at least until someone blows my doors off with a much better theory.
-Tacky