I had my first engraving done at AJI. It was a Colt 6920 SOCOM so I had him engrave caliber markings as well. The engravings were flaky and he was quick to blame the lower and told me I had bought a chinese knock-off as he had never seen that before. When I asked him to reblacken it he used a spray can of some sort and rubbed the paint all over the receiver.
I dug around a little bit more in the SBR forums and came accross CS223's thread. I sent him another lower and he did a phenomenal job with it. He engraved it exactly how I wanted it, reblackened and returned it within a week for around $40 iirc. No excuses or unwarranted comments. I posted pictures of the work in the thread if anybody is interested.
AJI is cheaper and local to us south floridians but I would only go there in an emergency. However I usually know ahead of time when I need to engrave a lower.