If i choose GA Shazam, are you going to ask a bunch of questions as to why?
Because the answer is, he (in Whiz Comics) was basically a Pre Crisis (Superman level) character with some Looney Toons mixed in.
I'm not going to look up a bunch of scans to back that up, sorry; as DS might say thats basic knowledge, and enough for me to choose him.
The members of the Marvel family were invulnerable to almost anything you could think of during their Fawcett Comics days, even to things like shrinking rays and magic, which would take down even the powerful pre-crisis Superman. Only possibility I can think of for a Thanos win here would be if there was some documented case of the Marvels succumbing to teleportation, hypnosis, or mind control.
Post Fawcett, both Superman and Cap were mind whammy'd into fighting.
Although Cap eventually shook it off himself, while Superman needed Cap to throw the fight at the last minute to break it (And Cap had him dead to rights, covered in metal fragments and set up for a lightning bolt.)
__________________ What CDTM believes;
Never let anyone else define you. Don't be a jerk just to be a jerk, but if you are expressing your true inner feelings and beliefs, or at least trying to express that inner child, and everyone gets pissed off about it, never NEVER apologize for it. Let them think what they want, let them define you in their narrow little minds while they suppress every last piece of them just to keep a friend that never liked them for themselves in the first place.