It's difficult to count every Marvel hero who's joined the Avengers, but the strongest two in the original team are undoubtedly Hulk and Thor. Bruce Banner's monstrous form and the Son of Odin usually share a friendly rivalry. Nevertheless, many Hulk/Thor clashes also involve ill intent and rage. With all their strength though which "strongest Avenger" has actually won most of their bouts?
Hulk and Thor began their rivalry in 1963, and it's still as present as ever in comics today. Fans can read the first Hulk/Thor confrontation in Stan Lee and Jack Kirby's Avengers #2. Thor comments on how he finds Hulk's appearance grotesque, and Hulk threatens to "boot him up to Asgard for good!" They'd continue their streak of battles in many of Lee and Kirby's series in the 60s, from Journey into Mystery to Fantastic Four.
Stan Lee, James Shooter, and Erik Larsen's The Mighty Thor #385 from 1987 marked the first time Hulk proved to be physically stronger than Thor. Even though Thor is still standing by the end of the comic, the Son of Odin appears destroyed. Meanwhile, Hulk is left unscathed. Larsen would return to write a rematch, along with Jorge Lucas' art, in 2001's The Incredible Hulk Annual #1. This issue marks a significant and historic Marvel moment, where Thor finally beats Hulk for the first time, fair and square. However, this same issue has Hulk recover and successfully knock out Thor before the end. It just proves that none of these Avengers' victories lasts very long; the two are essentially a perfect physical match.
For fans that want a definitive resolution for the Thor/Hulk battles, Al Ewing and Joe Bennett's The Immortal Hulk #7 delivers a more modern answer. The Avengers encounter a devil-possessed Hulk, who pulls no punches (not that the Green Goliath ever does anyway). Banner's angrier half immediately sucker-punches Thor, knocking him down in one hit. It's clear which of the two Avengers has more physical strength. When Thor wields Mjolnir, he can hit harder, summon deadly storms, and fly. But without his trusty hammer, Hulk genuinely earns the "strongest Avenger" title.
Hero Envy's John Cimino took the time and dedication to tally every single Thor versus Hulk comic book fight. Although these mighty Avengers have fought nearly 40 times in the comics, almost every match has resulted in a draw. Of the battles where there is a clear winner, the final tally gives Hulk a victory of winning a mere three fights over Thor's two. These stats mean that roughly 35 out of 40 times, Thor and Hulk are evenly matched (or only triumph/fail because of the circumstances). It's fair to say Hulk and Thor are equals, but, at least for now, Hulk narrowly gets bragging rights to claim he's "the strongest one there is."
Source: Hero Envy