As many have said, it all comes down to where you are, what the employees know and how much they care, and how well they keep their fish.
I will usually prefer mom-n-pop stores over any other place. My favorite knows me quite well by now and is always giving me discounts on stuff I buy, which I do appreciate.
If I just HAD to choose a chain store, it would be Petco. Although you can compare two here very well. Both are about a twenty minute drive away, so it's easy to compare which one is better.
The first Petco is sorta budding to the level of a mom-n-pop LFS but is not quite there yet. It tries to well-inform employees but probably would just end up giving them bad advice anyway. Last time I visited (which was a long time ago, I don't really like going to that one since they don't know a lot) is that a Petco employee was giving advice to a lady and her two kids about why their fish died. Although she asked if the tank was cycled, she ended up giving them the wrong advice about how all the bacteria is in the water. THEN she took out some test strips, put them in the water, they came out perfect, and said "That's what you want your water to look like"
Well....I wasn't very happy after that. Then she noticed me, helped me get a few fish, and started talking to me about her tank. THEN she pointed to a tank full of CAEs and said "I have two of those in my tank, love em!" I politely asked, "But won't they get too big for the tank?" And her reply was, "Nah, they'll just grow to the size of the ten gallon!"
At that point I simply left.
The other Petco is A LOT better. They have a nice variety of freshwater fish and will even get some unusual things from time to time. Although they have a few tanks with dead fish in them, as most Petcos may have, they keep the fish healthy and there are no signs of sickness. They have a variety of supplies, including some sweet T5HO fixtures, a selection of bulbs, hydrometers, salt mixes, API Test Kits, sweet stock on AC Filters and Aquaeon Pro heaters, even sand which the mom-n-pop LFSs around here never have.
They also have a small saltwater section dedicated to the store. I can't judge since I'm not saltwater, but it was pretty good for a Petco. They had one part of the freshwater fish section dedicated to a small, but decent, selection of saltwater fish. Regular pajama cardinals, ocellaris clowns, coral beauty, gobies. And although I don't speak for them and am not accurate since I am not SW, the fish looked in good shape.
They ALSO had a frag tank, which was pretty sweet. It was full of all asssortments of corals, though I can't remember which, I just remember it was awesome. They also had two levels of it, so there was corals on the bottom of the tank, and then a sort of bridge that held the high-light or high-flow corals. In addition, they kept some of their rarest fish in there too. I saw a mandarin goby, juvenille fox face fish, even a pair of firefish and an anthias in there on several occassions!
They also have a few cool display tanks. The best one is their 29G biocube, which is sweet, packed with corals, LR, even a real anenome! My only complaint is that I saw a tang in there (at least I think it was, perhaps a bigger variety of angel instead).
They also had a Fluval Edge, but it wasn't that good. They had a school of neon tetras, a DG and a betta, and a pair of platies in there. It looked quite overstocked to me.
They also have a decent plant section. Not anything rare or unusual, just your standard swords, mosses, java fern, anacharis, and the regular non-aquatic plants that come.
Will I be coming there again? YES!
