I voted drops, but it really depends on what kind of riding you plan on doing. If you are just dorking around, not going very far, then flat bars are fine.

On the other hand, if you want the fastest, most versatile setup, use road drops with hooded road-style brake levers. Bullhorns are a poor substitute for a good drop-bar road-lever setup. They offer some of the same hand positions but not all. Track drops on the street are idiotic. They are not intended for extended riding, are too deep, lack other good hand positions, and don't work well with brake levers.