[@Dead Cruiser] I want to point out just because it's Marvel/DC doesn't mean you need to somehow make an Amalgamation, infact Amalgamations aren't the point.  It's more "what if this Marvel character also had to deal with DC stuff " and vice versa.

Honestly there's still a lot of big names unclaimed. Superman, Flash, Hulk, Thor, Black Widow, Aquaman, Iron Man... 

Go with who you feel you can portray best and tell interesting stories with. If you don't want to leas any form of story build them to be a roamer, asking others to join in with what they've got going on.