One thing to keep in mind is that commuting boils down to a bike ride, just like any other bike ride. If you're a mountain bike guy you commute on a mtb. Racer types like to train on racing bikes. Anything you'd ride that distance is a commuting bike. My first advice is always to get the bike that you're going to ride, as opposed to any idea of "commuter bike" - it's just a bike ride.
The only things special about commuting is that you may tend to do it in weather that you might not venture out it for fun or training, you might do it in darkness, and it's usually (not always) a shorter ride. There are various ways of dealing with those factors, which may or may have to do with the bike itself.