Mike Tyson has got to be the right answer. An enthralling fighting style and unique personality combined with a sense of unpredictability. Even in the era of nutcase heavyweights Mike stood alone as the king of controversy.
Some i will say. Carl Thompson Amir Khan (always edge of the seat, some brilliant wars, Gomez, Limond, Maidana etc fights plus the ones he got KTFO) George Groves, the wars with Froch going life and death with Kenny Anderson then winning a world title late in his career. Danny Jacobs, got humbled early in his career, got cancer and came back like a new man. Marco Huck, wonderful career with a true caveman style in some absolute wars and nearly took Povetkin's head off. I could think of more.
Cotto? Fought many of the whos who around his weight class and was often in exciting big fights De La Hoya see above Pacquiao
Sven Ottke - Just a manic rollercoaster career with so many risks taken. He even boxed outside Germany (once - Austria).
Ali Raymi. He was a colonel in the Yemeni army fighting against the Saudis and he was knocking fools out with vicious body shots in round one, setting world records - no wonder Roman Gonzalez ducked him. It doesn't get more exciting than that.