I just wanted to say that the absolute,
#1 item for buying a new bike is buying the right **size** bike.
Components, brand, etc are all secondary. Even with brand it's only a difference between walmart/target brans and "real" bike brands. Basically if the retail price of your bike is $350 or more you're generally fine. I've had to replace a wheel on an $800 bike, but it's not like the whole thing broke down or anything.
P.S. Oh, and almost certainly if you commute for a while you will find it much easier to have a rack. You don't need panniers, but nearly everyone who commute finds that a rear rack bag is a lot better than a backpack. Rack mounts are so common as well, that I wouldn't buy anything without them.