If you’re running new game (not ng+), Deadpool, Hawkeye and Thor are must haves. It’s debatable in new game if Blade is worth the time to get especially because Thor kind of already does what Blade does but a lot earlier, albeit not quite as good late game. The fourth slot is very open, Ms Marvel, Doom, Iron Man and even Cap are great pics imo. The fourth slot is essentially just backup from your main damage dealers, Thor melee and Deadpool dual pistols, or your main support in Hawkeye buff.

Highly recommend running new game! So much more to figure out and different strats as far as XP farm goes and what to skip and what not too