I've ordered from airsoftparts.ca and ehobby.
airsoftparts.ca has great communication and service, I've gotten my stuff pretty quickly. The cost is a little bit higher, but I know what's in stock and on hand, and I can rest assured that my package will actually arrive. Plus I like supporting Canadian businesses.
Ehobby has been pretty good, but obviously some of the replica stuff in terms of softgoods is lacking in quality compared to authentic, etc.. Service wise has been good, packages usually arrive in 7-10 business days, sometimes even faster!
I've only had one missing item in my transactions with them (missing part from actual manufacturer), and they said they will be shipping it out to me on my next order (which I've just placed). Stay tuned for results.