what version of hulk is the most powerful
War Hulk was pretty powerful. More or less took down the Juggernaut with one punch. Stopped his charge also.
Worldbreaker Hulk was probably on another level. Onslaught punching Hulk is probably around here also.
But Giant God Hulk from the end of Heart Of The Monster has to take this since he was basically WorldBreaker Hulk absorbing a ton more Gamma radiation and swelling up to the size of Galactus. Given how much more powerful WB Hulk became without getting any bigger that implies a pretty big jump.
Uni-Power Hulk is nowhere close really.