Mine personally is Sage Francis or MF Doom.
I probably forgot some MC's or I just didnt think they were very underground.

Question:
Favorite Underground EMCEE?

Choices:
Buck 65
MURS
El-P
MF Doom
Sage Francis
Aesop Rock
Slug
Fatlip
Brother Ali
Sole

 

Although, I'm quite fond of Sage Francis and his colorful metaphors, I think one rapper is missing on your list: Doseone.

His wild stream-of-consciousness rap running from brain to mouth always take me out. The albums with cLOUDDEAD, Subtle and especially Circle which he did with Boom Bip are utterly amazing. In addition he did great things with Deep Puddle Dynamics, 13 & God and Themselves as well.

But of the ones mentioned I have chosen Aesop Rock. His lyrical universe is quite unique.

damn, i knew i was forgetting someone.

are you kidding me? Sage Francis is #1

Mf Doom is aite, sage francis is aite as well.my favorite is Madlib. His style is heavy and his rhyming ability is unique. Edon is sick as hell to he puts images in your head that he could only do. You missed sum underground

Boots Riley first, plus the likes of Elzhi, Raydar Ellis, Shad and Termanology.

Good to see the whole spectrum of the underground represented in the list.