Beta Ray Howard
Restricted
I say take it back to basics
Captain America
Iron Man
Hawkeye
Thor
Hercules
Wonder Man
Vision
Wasp
Hank Pym
Beast
Sersi
Scarlet Witch
More or less. I'd keep Dr. Strange out of it. He's a Defender, and needs to stick with it, all things considered. Him, Surfer, Hulk, and Namor are awesome as a team, though Namor fits well on both Avengers and Defenders.
The good question is what makes someone a good Avenger. I think more or less it's the bravery and willingness to take up the fight. I guess that the Avengers are essentially people that resemble what every American wants to be.
Now, most people who live outside the US probably think that's weak, but the companies do exist in the U.S. primarily.
Anywho, I guess it's just a level of strength and dedication that I honestly don't see in other books. The X-Men is more of a team to go against the norm. The Defenders seem to be the team that keeps the outer dimensional forces outside our home dimension, but seem to have a lot of tension, like a ticking time bomb.
The Avengers are more or less the typical American story of a team, though they're probably the most powerful team in Marvel as a whole, unless you go into dumb technicalities like "OMG TEH X-MEN HAVE DEAH PHEONICKS FROCE!"
That, and it seems that the Avengers have probably the most interesting character lineup, at least in my opinion, which I why Wolverine and Echo, or any other Ninja, need to be kept out of the picture. Hate to say it, but I may end up buying Mighty Avengers, provided they keep Ares quiet.