[Sundae]

I think I'd go with teleportation, but only if I could take someone else along.

That way I could have cheap holidays out of it, and not have my friends hate me if we had a late night drinking session ("Seeya guys! Just think, I'll be drinking a pint of water in bed while you're still waiting for the Night Bus!")

Though the ability to go back in a limited frame of time also appeals - never again thinking "I wish I'd said that at the time!"