I prefer GOG because of the DRM-free option, and I like what they stand for. But, you're right, there are a few cases where you'd want the Steam version instead. I'd say ask the community around the game and see what they think. There are no cases I'm aware of where not having the Steam version would be a problem, but I don't play games like that.

GOG does a few things better than Steam, though. They fix stuff. Steam just pushes what the publisher gives them. Two cases, same franchise... same shitty developer. Fallout 3 shipped with DRM called GfWL (Games for Windows Live), basically Xbox Live for Windows. GfWL failed, but Bethesda didn't take it out of Fallout 3, meaning to play Fallout 3 on PC, even if you bought it legally, you had to crack the DRM, which is illegal in the US. No one got in trouble for doing so, but that's what you had to do. GOG just took the DRM out. Problem solved. Something like a decade after Bethesda created the problem by not taking it out themselves, they did just that — VERY recently, and thus, it became "legal" to play Fallout 3 on PC again. Second case, Fallout 4. Same developer/publisher. Different case. They put out a patch about a year, year and a half ago, and it broke the random NPC generator. There was a cursed combination of variables that could make up an NPC, that if it generated that set of variables, you could never get close to that NPC, or your game would crash. Modders quickly found the problem and told Bethesda how to fix it. They refused. More to the point, they ignored the issue. I don't think GOG carried that update for months. They refused it. You could only get the older, last working version for a while. I think they eventually allowed it, but with a note on it saying it was broken with no fix in the works. Couple weeks ago, they said they fixed it... after like 16 months. But introduced more problems. (Disclaimer of bias: I own Fallout 3 and Fallout 4 and all the official DLC on Xbox, Steam, and GOG. I used to be a big fan of Bethesda, but after Starfield... I am discovering way too late that it's not a tenth the game the Mass Effect trilogy was. Better late than never, I suppose?)

Honestly, it depends on you, what matters to you more.

For their stance on DRM free and game preservation, Id buy from/support GOG every day of the damn week.

Problem is, that I'm from a third world country, with recent and very high inflation. Dollar is way too expensive here. (With a gov tax on converting the local currency to dollar on top of that 🤮)

So the above + regional pricing means I'm stuck to Steam + piracy.

If budget is tight, I'd say, stick to Steam. Otherwise, go GOG

I used to prioritise GoG but now I just use Steam for the Linux support personally. If that's not important to you it mostly comes down to whether you mind the inconvenience of multiple stores.

I personally buy from GOG almost exclusively, but it really depends on you. If Steam features are important to you, use Steam. If what GOG's doing with DRM is important to you, buy from GOG.

Can't you continue buying games from both? And use Playnite or something? Or even just GOG Galaxy which has the ability to import your games from Steam and run them?

I prefer Gog. I don't need cloud sync, I just want to download the installer and start playing. I hate the idea of needing a really heavy launcher like steam to play my games. I play via Lutris on Linux. DRM-free is important to me as a principle. I also happen to prefer Gog's UI when shopping around. I keep steam around for games I bought before I made the full switch to Linux and the occasional game that is not available on Gog.

Whichever is cheaper.

From both, but I prefer GoG. I bought everything I want to keep there. So I can store the installers, and won't have to redownload each time I install on a new system. But Steam has a smoother Linux experience.

GOG is great, but it would be silly to buy fighting games on there, for example, since it doesn't have any infrastructure to support their multiplayer.

Similarly, if trading cards or achievements are detrimental to your enjoyment, stick to Steam.

I stick to Steam for the most part because 95% of my library is not on GOG.

Depends on if it's a game I'll also be playing on the Steam Deck and not just on ny desktop. There is heroic launcher, but I prefer the Steam Linux experience.