Frank Sheeran is probably the guy with the highest body count, if you're counting the guys he killed in the war in addition to his hits. In a particular instance he claims he did 3 sepparate hits in the span of a day. He said in his book he flew to Puerto Rico and 'did what he had to do' on two separate matters, then flew back to Chicago and did another one. A busy man.lol

A few guys who haven't been mentioned:
-Lefty Ruggiero(27)
-Gerard Pappa(37)
-Mickey Featherstone
-Stevie Flemmi
-Johnny Martorano