I've had good experiences and bad from PetsMart. I bought my first betta, and two dwarf gourami's from them - all lived until my stupid accidents led them to pass on. They were all healthy. I bought two platies... Got nasty fungus and died... Thankfully none of the other fish got sick. Now, that was before I knew anything about fishkeeping.
I've been to PetCetera... One day while I was there looking at their bettas... Two or three of them were dead in their cups... I just moved them over to the stand so someone could do something with them. That made me really mad, because bettas are tough little guys! Their prices are also pretty pricey too... Can't say I'm fond of their fish either. Haven't bought anything there though.
I'm currently buying all my fish from a chain store - SuperPet. These stores have the nicest tanks I've seen around. Of course, these are new stores, but even the ones that have been around since last year still look nice. Of course, there was one koi swordtail tank that every time I went in, the poor fish were just dying off like flies... But, often times their tanks look good, clean, and the fish are bright and swimming around happily. All but one of the fish in my 33 gallon tank came from there, and they've all been healthy.
Unfortunately we don't have any local fish stores, otherwise I'd definitely buy from them!
