It's gotta be K.dot (Kendrick Lamar) he has such a wide variety of styles to project different feelings. (Ex. in "m.a.a.d city", he has this wacky, voice cracking, crazy voice that shows his passion to a place or subject... but in songs like "Bitch dont kill my vibe" or "i" he has this light nasally voice.) On top of that, his flow, in my opinion, is some of the best. He can also cover issues like racism or depression so well unlike any other rappers or other artists period. Just look at "for free?"
I really like threads like this... I had no idea so many people liked hip hop in the MLP forums