Avengers, because they've consistently put out better story arcs than Justice League. But that's more cos of the writers. I actually like the characters on the Justice League better individually, but the Avengers as a team tend to be more entertaining.`
Oh...so tough cuz I love heros from both sides. Batman is awesome but I love ironman about as much. Not entirely sure but just cuz a Justice League movie hasnt been made...yet, I'll go with Avengers, but if DC does make a justice league movie and its also extremely good, that might change.
I've never liked the Justice League and DC comics are always so....horribly written-unless it's Batman. Also those characters are such cookie cutter perfections that they seem more like self-insert dolls rather than complicated people. The only reason I would choose Avengers....is because of the movie version of Iron Man. He rocks it and practically makes the team it's own personality. Otherwise both comic versions...Neither, because while the movie is fine the comics shifts through so many characters in the Avengers....you can't really say to like it as a whole unless you like 90% of those characters. and obviously I'ved never cared for DC whose characters need more personality.