GOG support is awesome, while Steam Support was not really generous lately (no Dota 2 trading card for me, because I had spent $9 for Dota 2 items on Steam Market and not on the Dota 2 store, no TF2 gunpoint hat because I had bought the game from the dev rather than from Steam store). I am going to buy more often on GOG than on Steam.
A wise choice in my unqualified opinion.
