In my area, we have two LFS's and 3 Petcos. That is all there is for saltwater options here. The 2 PetSmarts in this area do not touch marine products or livestock at all.
That having been said, one of the LFS's goes from plenty of stock to almost none in a week's time, usually with little explanation (it's not all being bought, they are doing something with it like wholesale or something). You can go in at times and find NOTHING interesting on display. They do a decent job as far as keeping clean tanks and their setups seem appropriate. However, their pricing is way beyond appropriate IMHO. When they have them, small yellow tangs tend to be $90-100. Seems a bit much.
The other LFS has good stock for corals, but again, pricing is a big issue. Their hours are minimal and if you can get there when they are open, you're looking at things like a Royal Gramma for $75, etc. Hard to justify given the fact that you really don't get any better service there.
As for Petco, one of the local ones is a joke. It has really inappropriate setups, and little to no livestock at all.
The other two have nothing but reefers on staff, and they have full reef setups to display their livestock. Staff regularly turns customers away from buying things that would be bad ideas for that customer. Whenever I make a purchase, I am first asked what I have for equipment and who else lives in my tank. They do a great job and occasionally will call individual customers to let them know of a recent arrival that would be suitable for their reef.
Bottom line: with Petco, as with most other LFS's, it's hit or miss. I don't think it's fair to say "Petco always ______." or "I don't shop at Petco because they _______."