I've never been to KGS, but I really appreciate that he posts his inventory online. It's great to be able to know what's in stock before having to drive out there.
I think that for prices, I've yet to see someone come close to Danger Close Tactical. Unfortunately, he doesn't have a huge inventory. But I would definitely suggest taking a look, and like KGS, he has his inventory posted online.
I have no complaints about customer service from OGC, SEC, WGS, X-Ring, Young Guns, Honolulu Firearms... all have been very helpful, welcoming, and knowledgeable. There has only been one store that I've visited and I didn't like the CS, so I haven't returned.
Same with inventory: OGC, SEC, X-Ring, YG & Honolulu Firearms all have a large number of different firearms and supplies. I buy my ammo almost exclusively from OGC and SEC (and Sports Authoritah, when in stock) but mainly because I live and work in town.
OP, as to your follow-up question, I think it's hit or miss. Moosed got a great deal on his Sig, but I could save $300/each by buying my HK P30 & HK45 online (and that's after shipping + FFL fee). It's a matter of shopping around. Even if I might not buy the actual firearm locally, the money I save on the hardware goes to an LGS when I need an extra mag, or get an accessory, or for more ammo. That way I don't feel as if I'm screwing the LGS out of sales, but am also not screwing myself over by paying a 35% markup just to buy the firearm locally.