Walmart.com
The nice thing about Walmart is they do give you ample time before the pre-orders go live. Keep an eye on their twitter, and make sure you have an account setup with all your payment info ready to go.
What happened with me was as I was trying to order my Series X, I was in checkout and the entire website crashed, and when I finally got back in, I got the message of "there is no more of this item" despite the Series X still being in my cart.
Just as I was about to give up, Walmart sends out a tweet, saying that they're doing the restocks in waves and said there would be another batch in 5-10 minutes. So I basically sat on the Series X in my cart, until the restock happened and checked out successfully.
I don't know if they do that every time, but do be on the lookout for that. Myself, and nearly everyone I know who wanted a PS5/Series X and actually got one, managed to get one via Walmart. I don't know how they're different from the others, but it feels like the best spot to go.