man we have had this convo before...and ultimate colossus would have to go against ultimate Thing...who is about ten feet tall and has different powers than classic Thing....but if u want to compare the classic characters i think they fought each other....although I've never seen the fight...but when Thing was totally dominating a skrull doppleganger who he thought was colossus, he says the doppleganger is way tougher than Colossus should be. Also, when Champion of the Universe fought all the heroes of Earth, the Thing did far better than any others, including Colossus who just got his ass beat and couldnt even mount an offense...also, u never see colossus going toe to toe with the Hulk all on his own do u?...well at least he hasnt done it about 15 times like the Thing...i recall colossus fighting Grey Hulk, with the rest of the x-men too...I dont want to down colossus, he has fought Gladiator, and put Jugs on his but a couple times too...he's hella durable too...but the Thing is just too great a fighter, too experienced, and stronger in my opinion since he is continually getting stronger from any cosmic rays he's exposed to when he's in outer space or the Negative zone...colossus is really tough too though...he would put up a great fight but I doubt that Stan Lee would ever allow an issue to depict colossus beating the Thing, original strong guy of Marvel, who takes on guys more powerful than himself and wins through pure determination and toughness