The android Avenger! Of course you can’t have Vision without Ultron and that will come later. But Vision would be a great addition to the team. Make him more technologically adept, but still trying to be human. He’d be more like Data from “Star Trek: The Next Generation” — fully aware and willing to use his technologically advanced body to hack systems and such, but he’d be trying to understand human nature as well. He’d be a great POV for humanity’s issues. Can replace Iron Man.