i was just in both today. my local petco has healtheir fish, but they have a limited supply. they carry the typical livebearers, i.e. guppies, swordtails, mollies and a some tetras and a few other common egglayers. the water is clearer and the fish are much healthier. petsmart has a larger variety and they often have better pricing. the problem with petsmart is that you have to closely examine their fish for disease and just overall health.