Are you a fan of any one style in particular? The aggression of Cotto or Pacquiao, or the counter punching brilliance of Mayweather? The guile and craftiness of Hopkins, or the balls to the wall style of Morales? I personally love to watch lots of different styles, but I'd say my favourite style is that of Pacquiao. A high punch volume and sheer aggression, but always the ability to employ an in and out style, and also the ability to counter punch i.e. against Hatton.
The aggressive brawlers like Mike Tyson, Jack Dempsey, Joe Frazier (although Joe didn't throw enough punches). Of course, to be great at this you also need good defense, and you have to be careful when you attack. That's Rocky Marciano: the cautious brawler.
I like muthasuckas that enter the ring with all intents to win and refuse to back down and cower in defeat.
people who want to fight the best - even if they get there arses whooped brawlers like hatton, i do enjoy waching boxers like PBF and hopkins though
I prefer to watch a destroyer like Tyson with high percentage chance of a KO as opposed to a Calzaghe style who essentially wins by decision by outworking his opponent.
all of them, especially counterpunchers, as long as they have a powerful offense to go with their defense like b-hops, sal sanchez, jmm, and recently rigondeaux