Assuming the price is exactly the same on both platforms (or even within like $10 if I’m not getting a Steam key from the GOG purchase), I’m buying from Steam every time. Mainly for the convenience of having it in my Steam library, so I can’t just flat out forget that I own the game already when I finally get around to playing whatever it was, because god knows I don’t immediately play straight through the vast majority of games I buy.
Christfire would’ve gone hard.