Aah, back to the classic JR. high debate.
It is really hard choosing between the 2. Rakim is beyond revolutionary in both flow and content when you look at what his peers were putting out in 86. While nursery rhyme flows about bally's and Lees and whatever else was dominant, R replaced it with a slow delivery filled with conscious content that had brothers going to the dictionary. Equally, when Kane came out in 88 he brought Metaphors to the forefront with the added bonus of having 2 distinct yet equally powerful flows, staccato and smooth.
Album for album the debate doesn't get any easier. Paid in Full and Raw are both classic albums. The respective follow ups, Follow The Leader and It's A Big Daddy Thing are again classics. The subsequent albums give Rakim the edge as he maintained his presence while Kane drfted into the playboy role.
While it is an official crime to ever go against a fellow Brooklynite, I will have to vote for Rakim.
P.S. It was KANE who wrote all those Biz Markie hits as well as Roxanne Shante's and some of the Juice Crew releases.