Most advice will be to ride the bikes to make sure what fits and what doesn't. Schwinn's medium is not likely to be the same as Giant's medium.
Another thing to consider is, does the LBS have any incentives (free tune-ups for length of ownership)? The accessories can get overwhelming as well, so factor those into cost as well...pedals, shoes, helmet, gloves, etc.
I regret ordering my first road bike online, as the fit never really worked, I sold it, bought an older bike that I am learning to work on, and it fits a lot better. The more comfortable you feel on the bike may dictate how long you will keep cycling.
Good luck in your decision...a search may help as well.