Pac- I have to include him because he is the most Iconic rapper of all time. Not a huge fan of his, but I do have great respect for him (Shed So Many Tears is in my top 3 fav hip hop records too)
LL Cool J- His longevity was longer than Rakims and Kane. His impact was bigger than KRS'. He was Jay Z before Jay Z. His sales, although huge, doesn't match what he was doing in the 80's. People weren't buying rap like that then. He had double and triple platinum albums in 80's, which is incredible because it was still in the beginning stages.
Nas- The most creative of the 4. Longevity and classic albums. Story Teller, Picture Painter.
Jay Z- most successful mainstream rapper outside of Em.. Longevity.
Honorable Mention: Biggie, Rakim, Kane
I left Rakim and Kane off because of longevity. Its like they quit during the shift in hip hop. Something Nas and Jay handled well when era's and sounds shifted. Even LL did too when a shift was going from 80' to 90's.
Biggie, I think is top 3 MC's of all time, but he just doesnt have that much material. Career cut short