Well...some of 'em at least.
I just got in a shipment from the turkeys at Questar, no problems. First time I have ever dealt with them but I can tell right now these folks will do just fine. You get an 'A'.
Likewise, for mail order I have dealt in the past with the fellas at Wolverine and they were good too. An excellent source for the HK stuff in particular...and they get an 'A' too.
I am leaving this one out to the foolish firearm forum folk to decide: Marstar...I damn near ripped my hair out by the roots trying to deal with those people as I struggled to buy one of those chicom M14's. I gave up in disgust; three times they told me I was on the waiting list, and three times I got hosed! Now many of the other guys had great success with them but for me personally? I got treated like dirt and I am giving them an 'F'. Your mileage may vary and if so, I hope you got treated better than I did.
Next up is P&D. To me this is the benchmark standard in the business. The other guys out there may be as good, but they won't be better - because perfect is as good as it gets! Nobody can touch them for selection, nobody can touch them for service and they take this sport as seriously as we do! The only fault I could find with them (and this borders on nitpickery) is that they don't have much in the way of traditional black powder guns...but with that, they still come in with an A+!
It has been a pleasure dealing with most of these folks and I hope they are around for a long time to come.