I'd decide based on whether you're comfortable doing a little assembly and adjustment on the bike. If you are, those Motobecanes are pretty solid. At the shop where I worked, the comparable bike was a $530 Giant Via:
http://www.giant-bicycles.com/en-us/bikes/model/via.2.w/14852/66308/ (no rack though! The next version up has an internal hub and an OK basket at ~$600.) I don't think brand matters much for these bikes - a lot of them get made in the same factories and just have different paint & decals. Size is also not super hard to figure out for these - they usually don't come in very precise sizes anyways.
You could always ask your LBS what they'd charge to check it over for you -- that way you could save a little by buying the online bike, take a crack at putting it together, and if it just doesn't work out, have them do it.
Supporting the LBS is definitely worth something, plus you usually get a better warranty and maybe a free first tuneup or something, but I think it's your call to decide what that's worth. Also checking out the other LBS's is probably worthwhile.
FWIW my fiancee has the internal hub Giant Via, and absolutely loves it. Style is important - she rides it much, much more than previous "ugly" bikes that worked just as well.
Good luck!