Whenever I'm placing an order, I check my usual places and go with whoever is cheaper.
By and large, that has been NB and mostly due to shipping. Not always, but usually.
If that doesn't pan out any longer it will just give me the opportunity to try out a few new stores.
Also, I'm often ordering bulk DME (50 lbs) from NB and that does not (did not?) get the flat rate. Even so, their shipping has been consistently cheaper than other on-line places but they have the advantage of being closer to Chicago than most others.
I've never had a problem with delivery, but I'm not usually ordering just-in-time ingredients from on-line. For those, I run out to the LHBS.