I like fighters who both throw a lot of punches and possess some serious power. The best possible example now is Pacquiao.
JCC was a beauty to watch. He was just a great blend of pressure and timing. He knew how to land and land clean.
Since I am a long time hardcore fan I usually enjoy a tactical boxing match, but fights between two guys with high workrates, and at least a modicum of skill, can be pretty exciting. Pavlik and Miranda, two big middleweights, threw at a bantamweight rate. In the first round Pav threw 97 punches while Miranda threw 94 back at him. Someone mentioned Aron Pryor. One of the smartest things Pryor ever did was force Arguello to fight at a pace he didn't like.
Henry Armstrong is my favorite. Also, underrated in terms of skills. These high output fighters usually are.