First off we have to assume that Thanos doesn’t have any Infinity Gems/Cosmic Cube/1920s Style Death Ray of the week or this is a useless discussion.
Even then, the only reason I’m thinking this could be a fight is because of an event I’ve only read about, and wasn’t actually there to witness. Apocalypse apparently supercharged the Hulk, renaming him “War”, enough to smack the Juggernaut around with relative ease.
First of all, I’d like to know what the deal with this whole situation is, since I didn’t think En Sabah Nur was quite tough enough to supplement the powers of a big gun like ol’ jade jaws. Secondly, does this put him in a league with the Mad Titan?
Assume two battles. One where they meet by coincidence and their personalities just don’t “mix”, and another where they each have ample time to plan (but Thanos still can’t have any cosmic playthings.)