A PC game is either on Steam or GOG or it doesn't exist to me.
I subscribe to the humble monthly bundle thing and if a game doesn't activate on one of those two I'm probably never going to play it despite owning it.
I'd maybe have added epic to the list if it wasn't for the store exclusivity stuff. I know that they've dialled it back significantly, but anti-consumer stinks like that don't readily wash out.
Conversely, GOG is on the list because they're expressly pro-consumer, particularly with their preservationist initiatives. My monkey brain would prefer everything in one place on Steam, but I recognise behaviour I want to support in these companies, so GOG gets my money too
And make sure to avoid stores that actively promote the store exclusives concept, even for stuff that isn't an exclusive (anymore). They don't deserve our money. Looking at you Epic.