Man this is actually so tough. Overall I love them all quite a lot, but I think for overall consistency, it's Tony and Cap for being so great from the very beginning of the MCU, with Tony getting the slight edge for being so ever present in everything and always being so top notch.
Widow is probably next after them for consistency. Hulk is generally good but only really became great with Professor Hulk, and that's too late in the game to compete. Thor is generally good but became really great during Ragnarok. Too late to compete with the others but putting him above Hulk
Hawkeye.... is great all the time and has some of my favourite scenes in the MCU, but is just too sparingly used. I'd put him even with Hulk.
Iron Man > Cap >>> Widow >>>>>>>>> Thor >> Hulk = Hawkeye
The batman villians all seem to be one big joke that batman refuses to laugh at - SantaRPG