From my own googling, Carlin or Pryor may be considered GOATs, but there's no real consensus.
Jmo but the GOAT for 1950-2100 will come in the next couple decades. Standup is absolutely exploding and is becoming much more international (more entrants in a market just increases the odds) - it's simply amazing how many Indian comedians are popping right now, along with a few Chinese, Africans, Hispanics, and Europeans...oh and a LOT more women. It's not quite the 80% American-Jewish Male industry it used to be (a study from the late 80's stated this based on professional comedians). Not that it's a bad thing, but we simply have far more people from across the globe giving it a try. Similar to modern NBA, the increased competition raises all boats.
In the meantime, there's gonna be a lot of different opinions. I'll take Mitch Hedberg for my money, jmo.