A long time ago I finally pulled down my Jolly Rogers and stored my eye patch, due to GoG, since one of the biggest gripes I had with games (all the way back to the 90s) was the DRM in the official bought versions and all hassle and problems it caused (but not in the pirated ones, which made them a superior product) and GoG's principle since the very beginning was "No DRM" and they never wavered on that.
I also have the practice of downloading the installers for my games and keeping local copies - which GoG lets you easily do but Steam does not - since a long time ago and due to professional experience I became aware that if you don't have it in your hands you risk losing it for some stupid reason and now the problem is yours (are you really willing pay what it takes to take it to Court?) whilst if you do have it and they want to take it from you, it's up to them to justify it in a Court of Law (and, lo-and-behold, when they have to prove it rather than just update a row in a database to say you don't own it, suddenly it's not worth it for them anymore). I would say the various instances of shops closing and taking the user's entire (supposedly bought) collection or even just shops outright taking eBooks and films from the collections users had hosted with them and totally getting away with it have more than proven my caution on that.
I did eventually also got Steam and bought some games from them up until the point when a game I bought would not work and they refused to refund it (because I only got around to try it out more than a month after I bought it), at which point I stopped buying games from Steam (curiously, when I moved to Linux I tried that game out again and under Linux it works). Even without that, with Steam I'm always wary because they have more restrictions than GoG and possession of my games in Steam is theirs, not mine.
Anyways, my GoG collection is many times the size of my Steam collection, I'll always favor buying a game from GoG over Steam if available in both (even if I pay a bit more for it in GoG, as the way I see it a game for which I can download the installer and keep it forever is a higher value product than one were I have to trust Steam for ever and ever to exist, have a client for my OS and not do any shennenigans) and a game only being available in Steam makes it far, far less likely that I'll buy it.