I recommend the cambridgeside option. That's where I always go, but mostly because it's close by and accessable via the T (subway). Also, if you need any 3rd party accessories like speakers or a dock for your new iPod, they have a mini-circuit city and a best buy right there, but best buy is often overpriced so go with circuit city. Word of caution though, almost every "genious" I have met at that particular apple store has been anything but. So, best to ask your questions here (macrumors) before heading to the store.
Cheers,
Ado