Justice League in theory, since most of them are real superheroes, while majority of the Avengers are simply physically fit people in suits with no real superpowers. Thus these heroes don't deserve to be called superheroes imo.
But I guess I shouldn't consider every comic book movie as a superhero movie.
But anyways, the Avengers have much better movies so I would rather give my money to see them.
As far as who I like more, Justice League (mostly due to the animated series).
Who would win in a fight, Superman alone>>>>>> The Avengers. Add Wonder Woman, Green Lantern, Flash, and Martian Manhunter, and The Avengers wouldn't stand a chance
If it's a fight, Justice League. Martian Manhunter, Superman and Flash can do the trick without much help...
If we're talking about movies, well Marvel movies are better but Superman in the DCEU is a neck-snapper and heart stabber, and he has crazy mood swings so... I wouldn't wanna be in a fight against him.