I buy almost all of my games at Best Buy. The Gamer's Club makes them so much cheaper than everyone else. I picked up God of War today for $47.99, used the $10 bonus I got from Far Cry 5 (also purchased for $47.99), to bring it down to $37.99 - on launch day.
Best Buy is basically the rule for new games, unless I see a game that I want on a great sale on the XB or PS store (1-2 per year). Then there's an occasional used purchase from Gamestop (2-3 per year) or Ebay (2-3 per year).
The only exception that I've made to my Best Buy rule (since I joined Gamer's Club a couple years ago) is a digital purchase of Destiny 2 on the XB store. I knew I'd come back to it for DLC over the course of a few years, and the convenience of 3 years of not needing to load the disk into the console seemed to be worth the extra $12.
Edit to add: I also favor physical disks so that I can sell them afterwards. I sell probably 80% of my games after I finish them. I managed to keep my net gaming spend to under $100 a year for a few years this way. I'm above that number now, as I buy more games near launch. Still, gaming is a cheap hobby for me.
