Oof, that's tough. I don't have just one favorite character on Firefly, so I can't really vote, but I can narrow it down to a few...I'd say my favorites are Zoe, Wash, Jayne, Mal, and Kaylee. I know, that's pretty much everyone, but still. Zoe is just a complete badass, Wash is hilarious and adorable (as Alan Tudyk put it, he's essentially "Space Xander"), Jayne is too funny, Mal is very charming and sexy, and Kaylee is just the cutest. Really, I love everyone on the crew, although Simon and Inara bored me a bit at times and before Serenity, River could be kind of annoying.
I'll just have to find out which of my favorites gets the least votes and help them out.