I have four levels 60s and another one very close. Dr. Strange, Captain America, Daredevil, and the Punisher.
Strange towers over the other three so much it's not even funny. Daredevil might be able to crank out approximately the same single target DPS, or at least something close to it. But Strange does that amount of damage consistently to everything on the screen, has insane mobility, and he's very survivable as long as you keep his shield, reflect, clones, self-healing damage over time spell up, and astral focus ability when stuff really hits the fan.
Strange is the most complicated and active character I've played in the game out of the 15 or so characters I've tried until their mid-20s. The fact that he basically requires you to hack the .ini and add a second toolbar option to fit all his abilities in is mind-blowing. Sure, a bit of that is AOE incantation bloat, but every single ability of his is useful. Spamming his incantations is always a good tactic, but so is looking at the situation closely and knowing when to bust out certain abilities.
The main problem I have with Strange is he makes the rest of my roster seem almost boring by comparison. My goal was to level basically everyone up to 60 slowly over time, or at least get enough to that level to activate the 200% XP synergy bonus. And yet I find it difficult to play other characters after "maining" Strange. Daredevil and the Punisher are my two favorite comic characters and were a blast to play, but going back to them after playing Strange is a tough trade off. I constantly find myself thinking, "This would be so much easier/faster on the Doctor." I'm 95% convinced I should just start prestiging him and forget about the rest for the time being.
Gaz outdid themselves with him. Maybe I should give Silver Surfer a shot next. They seem to have really nailed it with the last handful of characters.