Thanos would defeat him. He is so much smarter its ridiculous. He is also WAY more versatile. Way too many ways to defeat Despero. Despero's only hope would be if Thanos didn't use his brain and just traded punches. But Thanos is way too smart for that. He beats most people without throwing a punch. He can outwit almost anyone. He made The Champion of The Universe look like a chump... and I put him way over Despero.
The problem with this fight is that the actual power levels of the characters don't coincide with what would happen in an actual comic. Bobby is actually much more powerful than the Hhulk, and can increase his density and size to the point where he is actually as strong or stronger than the Hulk. That aside, he could simply drain all water from Hulk's body, killing him instantly. Or turn his brain fluids into ice. Or his entire body. Then shatter it. There are a myriad of ways Iceman could win this fight, but in a comic, Hulk would obviously win, because if he was defeated by Iceman, a relatively minor player, it would debase all of WWH and most of Hulk's history and character as a whole. Realistically: Iceman. In continuity: Hulk.
Agreed if they fought in comics Hulk would smash, but realistically ice-man would own him.