Daredevil

Spider-Man and Daredevil have fought crime side by side several times in the pages of Marvel Comics over the years. Daredevil will exist in the smaller, more grounded street-level corner of the MCU, and Spider-Man could be the perfect middle ground between that and the more fantastical elements of the Avengers. Plus, pair Matt Murdock's radar sense with Peter Parker's Spidey Sense, and you've got yourself cinematic gold, as well as a few fun action set pieces.