NiP was formed right as CS:GO came out, meaning that they already had preparation coming into the game. In the early part of CS:GO, NiP set the meta and tempo with their own plays, while every other team struggled to figure out how to play the game as a team and how the meta worked. Nobody really believed in CS:GO's success but NiP and VG, which was why they were the 2 best teams in the world at that time. The skill cap was also a lot lower at that time, meaning that GTR could smash the opposition very easily. Now, in 2016 and 2017, in an environment where every team works 8+ hours a day, an environment where every player is more skilled than 2012 GTR, coldzera is able to show his dominance over every player with his AWPing, rifling, and pistoling abilities, along with himself being a support player and a great clutcher. It's very hard to exactly pinpoint who was the GOAT of CS:GO, but I believe it to be coldzera for those reasons. Maybe it is GTR, idk.