Brownell's by a slight margin. Have been ordering from them for at least 30 years, maybe more--never a bad transaction, even when the mistake was on my end. They just took that particular item back, no questions. Once they just said keep it and credited my card for that amount. Once in a while I check with the tech rep on something, too.
Frankly I use Brownell's as a yardstick of how a company should treat its customers. We need lots more like them.
On the more common stuff I give Midway a shot at it--but whoever gives me the best deal (and best service) gets my $.