I also like how armando had us believing Genis beat King Thor on the first couple pages...you can get away with murder for your favorite character until the right scans pop up.
I still think either Wanda at the time of Disassembled or Sentry/Thor. There might be some other chic picks, but those seem the most sensible.
Captain Mar-Vell was only ever an Avengers associate. He became an honorary Avenger posthumously. In the same manner Genis-Vell has only helped the Avengers out from time to time. Yes, in the Busiekian future, he's an Avenger, but at the moment he's not, and is dead, so he cannot be an Avenger. I will also not be taking the Hulk into account since he was removed outright from their roster and had Captain America placed retroactively in his stead as a "founder." Doctor Strange has never been an Avenger, he's helped out a couple times, but is one of the few people to outright turn down membership.
I'm going with
1) Thor
2) Wonderman
3) Gilgamesh
4) Quasar
5) Iron Man--now with his new upgrades he might be closer to the top, but we haven't seen how those upgrades come into play during Avengers battles, so I'll refrain from judging those.
6) Warbird/Ms. Marvel (as Binary she would be much higher of course)
7) Vision
That's just a quick list form off the top of my head. For that I was just taking into account basic super powers. Stuff like reality altering Wanda and the wildly powerful Sersi I didn't bother to rate, but let it be known they are up there. Also, Sentry is probably very high on the list, but considering the jackshit he's done as an Avenger so far, I didn't bother trying to rate him. Namor should probably be on there too, but he was an Avenger for all of five minutes.
And I know there are inconsistencies in my list, but whatever.