On the one hand I like GOG because it has no DRM and has better prices (in my country) than Steam and I have the feeling that on the one hand it follows more the open source philosophy than Steam itself, but Steam has helped enormously to play Windows games on Linux, so I haven’t really made up my mind.
On the one hand I want to buy on Steam for the convenience, but on the other hand I prefer GOG because (in my country) is cheaper. Which platform do you prefer and why?
To give an example, The Binding of Isaac: Rebirth is currently $15 on Steam with regional pricing, but on GOG it’s worth just $6.
You can add games to Steam to use proton so where they came from doesn’t matter. You can also use Proton forks and bypass steam altogether - much of the underlying tech is Wine; proton is a patched and optimised version of Wine not a stand alone Valve product. Its great what they’ve done but it is still a collaborative open source effort.
As for which store, I go on price and sometimes go with GOG even if more expensive because of DRM, and sometimes Steam because of the convenience of the workshop.
I don’t think it needs to be any more complex than that - these are company’s taking your money for the same product. Its kinda pointless being “loyal” to a retailer - its more important to focus on value for money and quality of service for each purchase.