Obviously it's a win-win for the fans and movie audiences, but which will be the clear cut "winner?"
It's really too early to tell, as the Justice League movie has no director attached or any cast, but let's take a look for the fun of it.
The Avengers 2
• Sequel to the blockbuster The Avengers
• Follows Marvel Studios' Phase 2 movies, with Iron Man 3, Thor The Dark World and Captain America: Winter Soldier; follows the Guardians of the Galaxy movie which looks to directly tie into The Avengers 2 with Thanos, the post-credit scene villain from The Avengers; may feature Ant-Man, as the Ant-Man movie was announced; may include additional characters: Ms. Marvel, Doctor Strange, more?
• Joss Whedon returns to direct
• Follows Marvel's Phase 2 movies: If they end up tanking, this is not a good sign for The Avengers 2.
Justice League Movie
• Similar to The Avengers movie, this will be the first time the Justice League is featured together on the big screen.
• Movie audiences are already familiar with a majority of the characters, sans maybe Martian Manhunter.
• Features the first appearances of all the characters except for Henry Cavill as Superman -- assuming no Leaguers cameo in Man of Steel (which at least one should, IMO -- and it should be Bruce Wayne, or at least The Flash).
• More movies will be spinning off this leading to huge audience anticipation.
• Everything is new; unlike Marvel Studios who built up The Avengers with their Phase 1 movies, the Justice League movie really only has the Man of Steel, and possibly Lobo, to create build-up. So everything is resting on Henry Cavill's super shoulders.
• No director attached: What's up with just about every director passing on the Justice League movie? Is Will Beall's script that bad or is the thought of going up against The Avengers just too intimidating?
• All-new characters: If the audience doesn't like the cast or the cast gives a poor performance, the Justice League movie is one-and-done.
• Unknown villains. Assuming WB doesn't go with Darkseid as Joss Whedon trumped that with Thanos, the main villain may be Braniac. This was another benefit of building up the franchise -- ala The Avengers -- audiences were familiar with Loki, but I assume not many would be with Braniac; however, maybe Braniac will be somehow featured in Man of Steel.
And that's my list of pros and cons for The Avengers 2 vs. the Justice League movie.
As far as the winner goes, that's up to you to decided, but The Avengers 2 already has a great track record to lean on; however, anticipation for the Justice League movie may be just enough to match that.
Let us know in the comments below which movie you think will do better and feel free to add to either of my lists above.