The Motherfucking World.
Nothing else will do.
Stop time to study and do homework, stop time to cross the street to eliminate any possibility of automotive accident, hell, just plain stop time when I'm doing any activity that doesn't rely on the laws of physics being active.
I effectively double, triple, quadruple my lifespan, and I gain that multiplier to however much I get done in my lifetime. Depending on how long I'm able to stop time for, I become nigh-immortal, pausing time for hours, days worth of existence (assuming I don't accidentally create huge vaccuums in the air or something upon unpausing time due to breathing while the flow of air currents are suspended).
All this, and I still have the option of Muda Muda, super-precision/reaction, etc.