The New Teen Titans and Guardians of the Galaxy
I'd love to see a story featuring these two teams.  I could see Robin and Star-Lord clashing over leadership styles, Starfire and Gamora sparring and  enjoying every moments of it, Rocket not amused at Changelings ability to mimic him, and so on.  Sure, there could be some villains in the mix, but the personal interactions are what would make this fun to read for me.