A great debate here trying to decide who is the greatest MC in the history of hip-hop. You really can't go wrong with either of these rappers. As uneven as many of their albums have been, you can't really deny that they are both in the elite echelon.
What strikes me is the complete dissimilarity of styles. KRS is more about politics and prosyletizing, with the occasional punchline-heavy freestyle. G Rap was all punchlines and storytelling. KRS had the deep voice and conviction; G Rap had the rapid-fire delivery and incredibly inventive wordplay.
If you put a gun to my head and asked me to pick, I go Kool G Rap. He is one of the five greatest MCs that ever lived (and the #1 underrated). He was years ahead of all his contemporaries in the early 1990s -- yes, including Kane and Rakim -- and paved the way for such lyrical technicians as Pharaoh Monche, Black Thought, Nas, Aesop Rock and El-Producto. Jay-Z owes a huge debt to Kool G Rap. M.O.P. basically took their entire style from his third album.
KRS-ONE has more cache and is considered more of a legend, but G Rap is the craftsman's rapper. And also doesn't consider himself the "embodiment of hip-hop."
Hell, I'm just glad it isn't the same tired-ass Tupac/Biggie debate. KRS or G Rap would destroy either one of those fellas.