Steam, GOG, UPlay, and Xbox
I mainly use Steam, but I'd rather use GOG since it's DRM free. When a game I want is on GOG and Steam I will always go for the GOG version. GOG has a lot of older PC games that Steam doesn't have and works on modern OS. Diablo and Warcrafts 1+2 got re-released on GOG. Fallout New Vegas is on GOG and Steam, but the GOG version runs better since it works on modern OS (Steam and GOG reviews point this out).
UPlay I only have cause I got Assassin's Creed Unity and Odyssey for free.
Xbox I have cause I got Phantom Dust Remaster and Cuphead on it, but since Microsoft is looking to put their games on Steam and possibly GOG I'll probably get rid of it.
I use Steam cause it's Steam.
I might give Discord Nitro a try in the future, but not now.