Well super speed means I'd have strong legs right? Super Strength never signifies where the strength is and I don't want to be tricked by a genie and have it be in my fingernail or something, while either way of super speed can't be a trick, I'm smart!
but seriously I'd have to go with speed it'd get me done with gym class faster and I wouldn't have to pay for transportation when I learn to control it, and I can still go to the gym for strength stuff anyways, I don't need super strength