We don't know what 155 GSP is going to look like, not to mention post-colitis diagnosis... So with that disclaimer, gotta say Conor is the tougher fight.
Nate is a crafty volume puncher, with an endless gas tank and good jits skills.... He is not particularly fast, nor is he known for his explosiveness or power. Standing, Nate is going to have problems, he lacks the power to keep GSP at bay, and he will not be able to fully commit to his striking, because of the takedown threat. On the ground, Nate does not want to be on the ground with GSP, it is the last place he wants to be. Georges will smother Nate, and beat him up. Georges is far too strong, and his relentless attack on the ground is simply the best in the world, at any weight class.
The only avenue that I can see Nate pulling out a victory is to outlast GSP, and hope he gases as the fight goes on... We saw Georges slow against Bisping, and that could have been a disaster... Nate is one of the most durable fighters in the world, and if GSP's gas tank runs dry, Diaz becomes a very real threat.
The difference with Conor is that he has 1 punch KO power, and that is what makes him a threat to anyone he fights, ask Jose Aldo. Conor is also lightning quick with his hands, which makes him dangerous when an opponent like GSP explodes in for the takedown. I don't think there is any real mystery here, GSP is a tactical master and even his dog knows that standing Conor is a threat, but horizontal the Irishman would be like playing with a baby... the trick is going to be getting Notorious on the ground, and that makes him a much bigger threat than Nate.
