Oh boy this is a great question. So I love marvel and DC movies and I would absolutely love for the Avengers Infinity war and Justice League to be combined into one movie.
It would be epic seeing Superman slug it out with Thanos, even though we all know that Thanos doesn't stand a chance. Can you imagine how cool a fight between wonder woman and the Black Panther would be??? It'd basically be Wakanda against the Amazon's but between you and me I think I'll stick with the Amazons.
Captain America would probably clash with Batman on who should be the leader and when Wonder Woman is done making short work of T'challa she'll probably face off with Thor!!!...my money is still on Wonder Woman though.
Iron man Vs Cyborgs would be quite the battle, I honestly can't call a winner hear and the Flash and Spiderman's humour would just end up making the movie super funny too.
The movie would be epic because when they're done with they're petty squabbles, they'll join forces and take down steppen wolf and Thanos togerher!!! That my friend would be an epic movie!!!