Steam, but that is because of my approach to games and I do understand it is leasing/renting, not literally buying.

While I do enjoy going back and playing some games, most tend to lose my interest due to newer and improved versions of similar games. Nostalgia only goes so far when janky controls get in the way.

I also like a wide variety of games, but they are hit and miss on personal enjoyment. So what I prefer to do is buy several on a sale and then as long as one works out I came out ahead! This generally means I can check out games that are 5 to 10 or more years old at a heavy discounts due to being patient. I don't even bother refunding the ones that don't work out because most are a few bucks and if a few bucks let's me check something out then I'm fine with that.

For that cheap pricing I get all the benefits of digitally distributed games that are reliably updated to run on new hardware, can re-download them at any time with no limits, get the other hit and miss benefits like friends and forums and other stuff. They don't take up physical space, have regular updates, and addressed all the issues I had with gaming back in the 90s/early 2000s when still buying physical games.

I see it like a rental with no return date. I would probably quit gaming if steam goes under or changes enough to make it less convenient. Still hope that physical distribution sticks around for those that prefer it, and that other distribution sources like GoG stick around and are successful for both completion and for those who have different priorities for gaming.