Perhaps one of the longest running rivalries in Marvel Comics... in superhero comics as a whole, is The Incredible Hulk vs. The Thing. Going all the way back to Fantastic Four #12 and perhaps more significantly their full on battle in Fantastic Four #25. Hulk is clearly the stronger of the two (by a log way) although Thing has never quite been prepared to admit that fact.
This artwork by uncannyknack shows the two titans going one on one right in the middle of a city and while they're both in good shape, everything else is collapsing around them.
Remarkably this powerful art is billed as a work in progress.
Source: DeviantArt - TheThing vs. Hulk