I say 7 is the perfect size team. Grant morrison's big 7 in the JLA was great, iconic, and still had a fresh feel for the characters. So we have to have the trinity........
Captain America. Steve Rogers, the leader, the heart and soul. Gotta have him on there.
Iron Man. Tony Stark, tech, humor, and general pompousness are great.
Thor: The classic, the powerhouse, the guy who inspires awe when he walks in a room and fear among the bad guys.
Jean Grey. The young one. Not alot of TelePaths in the avengers, throw in her future as the phoenix and its a good ongoing well of future stories. As long as it not overdone.
Spider man. Miles Morales, he is the spider future, so lets give him a shot.
Human Torch. He's available and has tons of experience. Always and optimist, and plus he could really give Miles a hard time since he and Peter have always been close.
Warrior Woman. Hyppolyta from the secret defenders run. Granted, she is a wonder woman analogue, but I would like to see her interact with the rest of them, and how her powers given by the death gods drives her.
I would have put Black Panther in there, but we are being inundated with him right now. Its just too much. And I guess there is no way a plausible reason could be made to get Taskmaster to do (reluctant) hero's turn but I think that would make for a interesting storyline for certain.