I preferred the large Canadian bookstores.
Small bookstores typically just don't have the selection, and American big bookstores seemed...standoffish? It can be really hard to describe just in what way it was less pleasant. Part of it is a structure that encourages you to read lengthy passages in the store back home that I haven't seen in a larger bookstore in the US. I fully admit I haven't travelled the length and breadth of either country; I'm just going with the places I've been.
I go to Amazon for something that I knew I wanted ahead of time, which is relatively rare but if I accidentally start reading an unfinished book series it will happen and Amazon tends to be clearly the best option. And with the stores I like closing down, I now go to Amazon also because it's the best available.
The "World's Biggest Bookstore" (that's a name, not a description) in Toronto, as seen on the movie Short Circuit 2, just recently closed and that is probably the thing that will shift me over to using Amazon near-exclusively.
Although interestingly a lot of the long tail books aren't directly available from Amazon itself, but are available on Amazon.com via its partner re-seller programs, some of which are also big warehouses but some seem like smaller businesses that are just supplementing their incomes. Usually these are out-of-print books with "used - like new" tags as I try to complete things that I read as a kid from the school library, which was incomplete either because they didn't buy the full series, or they did buy it and a kid wrecked one, or the series wasn't completed ~15 years ago when I would have read them.