In MMA i'd break it down to styles so for
-boxing I'd say Rampage and BJ
-Muay Thai I'd say Anderson, Cung Le(well San Shou I guess) and Thiago Alves
-Karate: Lyoto Machida Hands down.
-KO striker would have to be: Chuck and Thiago.
-Ground and Pound striker: Randy and old Rampage.
-Best overall striker encompassing KO power, technique and accuracy would be: Anderson.
In Kickboxing K-1: Alistair Overeem.... JK. Young Buakaw.