I've purchased from Lucky Gunner quite a few times. Excellent, fast service. And they stand behind their goods. They sell a brand of loose packed bulk ammo From Military Ballistic Industries. It's remanufactured, and really cheap. I bought a bag of 9mm. It turned out to be crap. The cases were dirty and corroded. Some were split open, or had dents. Horrible quality. I complained to Lucky Gunner and they refunded my money. Didn't even ask for the stuff back.
As to Cheaper Than Dirt, my experience with them has also been good. Fast service. Reasonable shipping charges. The main complaint a lot of people have with them is that the during the ammo shortages in the period following Obama's election, they did some price gouging. Charging inflated prices for ammo. Some have called for a boycott of the company because of it.