For myself, I’d love the power to fly… I wish I wasn’t scared of heights, though.
As for the most useless power, well, I’d have to go with some of the powers from the game “Stuperpowers” (which was short for Stupid Superpowers. Urine of invisibility (urinate on someone to turn them invisible), Locate 24 Hour Convenience Stores (anywhere), Make all the world’s cellphones ring at the same time, Turn wheat products into cocaine, Create 3 Cubic Inches of Mashed Potatoes, Summon Mariachi Band, Give anyone hairy palms and blindess, Flatulence of Life (Your farts make dead people live again!), Create 70’s Hairdos…