JohnnyChin: I see some post mentioned GOG you can link your steam account to get same game on GOG for free, does it available for all game that both platform have?
Kardwill: Nope, it's just a promo that happens sometimes for a few games at a time (and only available during the promo, i.e. only if you ask for it during the event)
You have no way to know if a game will ever get that promo, or when it will happen, so don't count on it when you buy the game. (Which makes sense : GOG would never sell a game if people knew they can simply buy it on Steam and get both)
As for "which is best?", the game is the same on both platforms. GOG tends to be a few days late on patches for a few games due to its QA controls (but has less chances to get game breaking bugs on the latest patch as a result), but otherwise no difference. Mostly depends on which store you want to support, and if the handy DRM free installers are something you want.
yeah, of course, I like DRM free, hate every time I have to launch Steam to play a game, event a small game, but steam always cheaper than GOG as it use our country currency, I have 3 oldie game on gog, and I like to support GOG, so yeah, I think I will wait for sale, since I don't have to money to spend something other than my daily need now, only can watch people play or now, awww. Hope those reddit generous people who give Stardew Valley to people who can't afford still exist!