Armin. Even Erwin had recognized that Armin was able to piece things together that Erwin himself couldn’t see, which is why he chose him to lead the corps during the recapture of the wall mission. Levi also had known that Armin had dreams beyond the walls - Erwin had nothing beyond just getting to the basement.

Also, just an afterthought here, I feel Levi couldn’t bring himself to revive Erwin while Zeke still ran free. It was Erwin’s last request of his life to take the Beast down, and Levi failed to ultimately kill him. I personally don’t think Levi could bring Erwin back to a life where the sacrifice of the entire survey corps didn’t have the outcome they desired.