Haven't really thought about it.
In no particular order.

- Black Thought

- Kendrick Lamar

- J. Cole

- Royce da 5'9

- Eminem

- Lupe Fiasco

- Lauryn Hill

- Jay Electronica

- Phonte

- Masta Ace

Honorable mentions to Lil Wayne. Don't like much of his music but dude is a beast. Same for Nicki Minaj. She got mad bars and ill delivery. Can't front on her.
And then Drake. Yeah he may not be writing all of it, but to be so consistent and on top for this long....and bounce from one genre to the next...whether it is hip hop, dirty South, or pop. It takes skill and a diverse ear.