When i went to NY a while back, i went in a few shops in there and to be honest with you the selection is shite. it's only good if you're looking for old tunes really. They were well behind us on the release front thats fo' sho'
Trainspottersmusic.com is a pretty solid physical/online store in Boston. Definitely stopped messing around with Breakbeat Science and Dance Records cause trainspotters simply comes through with ALL the latest promos before they are even catalogued on other sites.
As far as a stateside record store I've never come across anything else that is on top of current releases. They also have pretty solid customer service which I can't say for breakbeat science.
Like everyone else said though, it ultimately depends on where you're going to be in the states.