Well depends where you look.

ESPN did a list not to long ago I'll see if I can find it.....

Heres BoxingRecords top 10

1. Muhammad Ali (56-5-0)
2. Rocky Marciano (49-0-0)
3. Gene Tunney (83-1-3)
4. Joe Louis (69-3-0)
5. Floyd Patterson (55-8-1)
6. Larry Holmes (69-6-0)
7. Jack Johnson (93-14-12)
8. Harry Wills (79-10-4)
9. Joe Frazier (32-4-1)
10. Sam Langford (200-47-46)