Petsmart is way better (at least in my area). The employees know a lot more about fish, the people at Petco are absolutely clueless, its really BAD. This one girl especially has ZERO business working in the fish section, she has no idea about anything fish related. I asked her if they had any 20 gallon Highs and she said, "What do you mean by 20 gallon Highs, never heard of that". So the next time I went in there, I decided to mess with her a little. I asked her what she could tell me about fishless cycling. Same response, she never heard of it.
The next time I went in I asked her if African cichlids would be ok with bettas (obviously not) and she said, "yeah, I guess". That was just too much for me. I went home and called the manager of the store, we had one of those come to Jesus talks, I was pretty blunt with him. She still works there but they won't let her anywhere near the fish now!
The only reason I go to Petco is because they are a lot closer to me than Petsmart, I only go there for supplies, never bought a fish there, nor will I ever.