For me, after watching Matilda, I always wanted telekinesis. I think the movie really resonated with me for other, more substantial reasons, but I remember as a kid wishing that one of my high-stress situations would let me get those powers.
Edit - Fun fact: I had a sibling who stopped believing in God because they prayed for Wolverine claws as a kid, but didn't get them.
Telekinesis gang as well. It covers so many other powers, super strength? Why bother, I'll use my dang mind to move whatever. Flying? I'll just lift myself with my awesome cool brain. If I could get real precise with it I could just split a fucking atom whenever I felt like it. Best power.