My opinion is a flat bar road bike.

I've used a hybrid, but felt it had too much resistance on the road. While stepping up to a road bike it was much better, and I love the drop bar. Just feels great on the road, low resistance, both wind ánd asphalt. However, if I were to commute IN a city, I would be using a flat bar. It's just more comfortable I guess, and should be easier to brake (I think, comparing a road bike to a hybrid). As well, you will be just slightly more upright, giving you just a bit better overview.