I like anything that works with a finish as the goal. And guys with excellent cardio.
I hate anything that serves no other purpose than winning a 10-9 round. And I am really disappointed when guys gas too quickly.
This.
I don't mean to sound like a douche, but I like watching very good fighters.
If I were forced to pick a favourite style, it'd be creative, aggressive striker with a wicked guard/sub game, a la Condit, Pettis, Cerrone. But I also really enjoy someone who's incredibly well rounded, like Aldo, Jones, GSP.
But basically, if a fighter has really fucking good, effective MMA style, then chances are, I'll like it whatever it is.
I love watching Jones, Brown, Cain, Pettis, Condit, GSP, Anderson, Aldo, MM, Rousey... they all have very different styles, but they're all very good with their styles.
Pretty much the only thing I can't stand is timidity and/or safe but ineffective game plans. Strikers who turn in to Sparrers because they're afraid of the takedown. Or wrestlers who are great at getting someone down, but then just die in the guard once they get there.
You're there to fight. Fight. If you do, chances are I'll be somewhat of a fan.
I enjoy watching greatness in action.