You then have to build your universe around them. You get associated characters to bring in. Would you make a team? What fights would you set up?
I'd pick Captain America, Namor, Black Panther, The Batman, Wonder Woman, Green Lantern: Alan Scott
This would give me the Invaders to play around with - Cap, Namor and Alan. Wakanda, Atlantis (Marvel), Theymiscra.
Cap vs Batman fights. Namor vs Wonder Woman.
Red Skull, possibly the Oans, Batman's rogue gallery.
Which fight would you like to set up?
Punisher-Gritty street level characters that would bring a since of realism to the universe.
Doctor Doom-Because Doom
Adam Warlock-Cosmic, infinity Stones, etc