A lot depends on your preferences. Do you want a road bike? For speed, that's the natural path, but if you don't like the riding position you can still get speed benefits with a cross/hybrid. How much are you looking to spend?

The first thing I looked for in buying a new bike for commuting was suitablility for rack and fenders. A lot of the faster bikes don't have good rack and fender support on the frame. So that cuts down the size of the field right there.