Which character would be harder to stop.

The planet would cease to exist if Hulk was on Earth

Hulk most likely, since he can punch planets.

Def hulk the avengers can take down giants

Hulk. His mobility would be a pain in the tail feather for militaries to effectively track.

Godzilla is so big that you can keep trying out different things and throwing it at him because you always know where he is or which direction he is headed. Evacuations would be easier to manage too. Hulk does million mile leaps and it's back to square one for getting troops, armor and supplies in place to engage him.

Probably Hulk. Don't lowball Gojira though.

hulk