For me, it'd probably be teleportation. The possibilities with teleportation are basically limitless.

• Building's on fire? Teleport in, grab the people inside, and teleport out. Easy.
• Getting your butt kicked by a supervillain? Teleport to a gun shop, grab some weapons, and teleport back for round 2.
  • Alternatively, just grab your opponent, teleport in front of a moving train or something, let go of your opponent, and teleport away.
• Need to defuse a bomb? No need! Just teleport the bomb to the middle of the desert. Never worry about cutting the wrong wire again!
• Want to go to a Taylor Swift concert, but you overslept? You guessed it: just teleport! You don't even need to buy a ticket!

Admittedly, stopping time is another very useful power, but teleportation is just really hard to beat. What say you?