One thing that I have learned is that your first bike will not be your last bike, remember that. You will learn what you like and dislike as you go. Give it a couple of years trying different bikes and different riding positions on those bikes. You will know what is right for you in time. Also know that you interests will change as you become a stronger rider.

Buy cheap at first until you know what you want, then upgrade and sell off the old ones. I'd suggest going used for awhile.

Take my case as a commuter in Chicago (flat ride, 10 miles each way) for nearly 2 years now. I started with a comfort hybrid (specialized crossroads), then went to a flatbar roadbike/hybrid (specialized sirrus), then to a single speed track bike (Dawes SST), and now finally on a fixed-gear 'hybrid' (Kilo-WT, fixed-gear, road bike frame with hoods/drops and touring wheels).

I would have never considered this bike two years ago but could not be happier now.