My power would be Look of Fluff, if you look me in the eyes, you transform into a Fumo, permanently. (Joking! Real power below.)
The real power i would choose is: Gravity/Mass Control
With that power, any incoming attack is easier to defend (just make it heavier/lighter before it reaches you) and put sturdy objects in orbit around me.
It's also good for offense, i can alter my body's gravity to pack more power in physical strength, throw objects with altered gravity or just end the enemy by making its head weight like a car.
There are practical uses, like carrying heavy objects, flying, stopping mosquitoes at bedtime (you make them crash against the floor) and more.
This makes me think why this power isn't more used in fiction, i can't remember any fiction where it's used.