Do you have any cycling interests beyond commuting? The reason I ask is that you can do a 4.5 mile flat-ish commute on pretty much any bike. Given that, I'd think about how you might use a bike recreationally.
If you're stuck between a hybrid and a road bike, you might be interested in a flat bar road bike which kind of splits the difference.
Test ride a few bikes and let that help make your decision.
If you were in a wet climate I'd definitely lean towards disc brakes but seeing as how you're in Nevada I wouldn't worry about it too much.
Last edited by tjspiel; 07-07-11 at 12:15 PM.