Good question, I'll post some now and expound on it later.
So much of fandom is not only subjective but irrational. I've only met a handful of fighters and only have secondhand knowledge of a few more, so like everyone most of this is gut feeling.
Frankie Edgar, love the heart of the little guy. He's still champ in my book.
Pat Barry - Pat always puts on a great show, he comes off as a very genuine likeable guy and from what I've read he will spend more time signing autographs than any other fighter.
Randy Couture - He's everyone's hero.
The Miller Bros - Those guys are class acts all the way.
GSP - That guy may not the be the most excited anymore, but he's a great champ and a wonderful ambassador to the sport.
Chael Sonnen - That guy's nuts, but he's entertaining.
Roy Nelson - Brings a much needed sense of humor to the sport. Great chin, great heart, great overhand right.
I'll post more later.