It isn't either or. If the local store supports the hobby, I support the local store. If it's an impersonal chain that sells the same crappy farmed fish as most of the online sellers, no, I buy elsewhere.
I have 3 local stores. One is full of the staple fish I'd get online. But I can go there and look at them. I can spot problems, avoid tanks and make informed choices. Online, I would buy blind.
The second, conveniently, is a step up. They are mainly mammal supplies, but the selection of bread and butter, ordinary fish and plants is good, and they use a supplier who gets them better fish. They're locally owned, and old school enough that they bring in the occasional oddball. Their dry goods cost a little more, but i want them to exist for those times I discover a need and have to run out.
Store three is small, wonderfully run and super responsive to hobbyists. I wish every town had a guy like the owner. The fish are run of the mill but good, the dry goods have good DIY options, he'll special order, he sells live food cultures and everyone working there knows the job well. They work directly with local planted tank enthusiasts to package up their plants and sell them.
The "market" alone is a destructive force in our hobby. If price is all that matters, go online. Buy sight unseen. But remember that a good store is a useful resource, and the chains answer to shareholders, not customers. If we allow the real aquarium stores to be strangled, we are left with glofish, hybrids, fish tb and bad info.
I can be a hypocrite because I am a longtime hobbyist with a network, and still get a lot of fish directly from an importer I've worked with. I don't buy farmed fish, and I don't buy fish I don't try to breed. I have fish from other breeders and importers. But for plants and dry goods, if I can get them locally, I do. Online ordering is a last resort.