Superman has had to hold back his full might for so long that it is reflexive to him.It is second nature.I don't think the Hulk ever held back unless it was the smart Hulk.There is the argument that Supes superspeed would leave Hulk behind but the Mindless Hulk once faced Quicksilver and just grabbed his arm by anticipating his next move and grabbed him.The old school Hulk even caught missles out of the air and they must have been traveling as fast as Superman's superspeed.The Hulk simply can snatch you out of the air because he has acute hearing and instinct.The Hulk may not fly but his sheer leg muscles made it possible for him to move through the air and maneuver like an agile bumblebee.Superman can move planets but put a space helmet on Hulk and direct him toward a planet and he probably could move it too.He probably could cancel the planet's gravitation and rotation if he really set out to it or at least smash it to asteroid bits trying.The Hulk could probably grow when his anger soars until he is the size to do it.Superman has always stated that the Hulk was the strongest mortal he ever fought both times he fought the Hulk.So unless Superman flew the Hulk into the Sun I don't see the Hulk quitting until he smashes PUNY CAPE-MAN!!!!
I know it may not be the most popular aspect of his character, but WWH did show that Banner is always "doing the math" in his head to prevent anyone from being hurt and always holds back. Based on that, the only times you'd ever really have the Hulk not holding back would be when he was split from Banner. By that criteria, the Hulk seems to hold back more often than Superman (who's really only cut loose a handful of times.)