In a new interview with IGN, Larian Studios boss Swen Vincke responded to questions about Baldur's Gate 3 being on Xbox Game Pass, explaining why the best RPG of 2023 won't be on Microsoft's subscription service anytime soon.
The main benefit GOG provides is their installers, which you can backup yourself. DRM-free Steam games don't, so you'd need to package up the files yourself (usually all in the steam directory).
That's not a huge advantage imo, so I generally take the convenience of Steam over GOG, especially since I use Linux and GOG hasn't bothered to port their client to my platform. Regardless, DRM-free is better.
I use lutris to manage my games, which is decently integrated with GOG. I ended up installing Galaxy for Baldur's Gate 3 because of the frequency of updates, but I mostly use the installers directly.
I prefer to buy from platforms that actively support me instead of leaving it to the community. Valve invests a lot of time and money into improving Proton/WINE, and they build in useful features like controller configuration into their platform.
If GOG supported Galaxy on Linux, I'd probably buy more from them. But they don't, and I have a Steam Deck, so I prefer Steam.