Being really strong and being a good puncher are two different things, which is why I brought up Rogue. Superman might have a poweful blow, but that doesnt make him a good puncher. On that list, Namor and Thing both strike me as the best punchers. Thing trained up in boxing, and Namor has always had a impressive haymaker. They might not have the hardest punch, but they are probably the best strikers on that list. If Wonder Woman were included, I'd say she trumps them.
Superman and SMP especially are just sluggers. They rely on strength more than technique. Iron Fist is nasty, but he is asking for guys in the class 100+ range, who generally dont rely much on skill. Thats why I like Wonder Woman, shes obscenely strong but has ability to go along with it, which is rare in that class.