As a huge fan of Darren Aronofsky's movies, I second the Black Swan, Wrestler and Fountain recs. I love ALL his movies, I did a re-watch of all his movies a few months back and was engrossed and entertained at various levels by them all.
Pi is the only one that is a bit rough around the edges but still a great watch. I'm probably one of the few that loves Noah. His last one The Whale was excellent and a bit different from his usual cinematic movies, which I read was intentionally made to feel like a play. I too don't have a favorite one but I'm very partial to Black Swan, it's so hauntingly beautiful.