If you had to make a list, which super-heroes would you say are the most realistic and why?
Punisher. He has no powers, lives in a real city, doesn't really have a secret identity, and mostly fights street crime.
Green Arrow. Also has no powers. Has a believable origin. Currently operates out of a real city. Fights mostly street crime.
Batman. No powers. Believable origin. Believable base of operation. He loses points for living in a fictional city and having a somewhat unbelievable rogues gallery. Best example would probably be Earth One version.
Iron Man. No powers. Somewhat believable origin. Sufficiently advanced technology would allow suit to be created. Lives in a real city. Strikes against him would depend on how advanced his suit is. Obviously the kind that fits in a watch like the movies is out. Or the Extremis suit. Fighting terrorists and groups like AIM or Hydra isn't too unbelievable.
Black Widow. This applies largely to the movie version. A specially trained fighter who used to work for the Russian government and now is an agent of SHIELD is believable. The WW2 origin would be out.
Daredevil. This works with the suspension of disbelief rule. A kid gets doused with radioactive waste and loses his sight. In the process he gains a vague "super-power" of heightened other senses.
Feel free to pick others you may think I forgot and making your case for why you think they are "realistic".