Riding at a higher cadence has many advantages, and is almost always a better choice.

*You have more control over the bike
*It places less stress on your joints
*It emphasis the aerobic system over muscular force, which will always fatigue first
*Functionally, most riders produce the highest sustainable power (for every time duration) at higher RPM's.

Those things I mentioned above are for efficiency, and safety reasons. If you don't care about efficiency or safety, then don't consider my points.

If you're just stomping down a few blocks, or having fun, then your gearing won't matter so much. If you're riding more than a few miles, a lower gear will probably make you capable of producing more power and make you go faster.