And I think character creation is a lot of fun! Some of the best character creation sessions I've ever had was with Traveller.Traveller. Whedon said Firefly was based on an RPG campaign he played in college. He's never said which system, but it's pretty obviously Traveller. Hell, in the scripts for the show, he spells traveller with two l's here and there, rather than in the American single l. So, why not go to the source? It seems the obvious choice for the most "authentic" experience., IMO.
One of my favorite things about Kevin Crawford's stuff (and I own all of it, or close) is that it's still really useful even if you aren't using the default system.