A frequent contributor here AdamDZ has a blog he just started. He has some good info you might want to check out. Its called NYC Bike Commuter (I am unsure if I'm allowed to link the site or if its considered bad policy to name it. If so I will edit my thread. You may want to message him).

As far as your buying choice goes It depends on what you plan on doing. Will you commute and carry stuff? Will you want to do some distance work? Do you want to go fast? Etc, etc, etc.