I'm afraid I'm across the country so I can't point you in the direction of a fish store. Google can turn up some surprises though!
As for what I prefer, it depends on what I'm out to buy. I prefer petsmart for decorations and plants. They always, always seems to make petco look stupid when it comes to plethora of choices for caves, aquatic foilage and chemical/water additive needs. Petco, however, makes petsmart look stupid when it comes to picking out a betta to bring home with you that day.
My local mom and pop pet shop is where I go when I want top notch plants but they seem to have them so rarely that I just gave up and went to petsmart.
So all in all, I probably frequent petsmart the most. They're the cheapest and have the best selection. Their employees could be friendlier but whatever.