AZ - Not really a fan besides Doe or Die and his features. Can't name anything memorable he's done in the last decade
Canibus - Same as AZ. Never been that big a fan.
DMX - Hasn't been relevant since 05 so I don't think he qualifies
Eminem - Only bad steps he's taken were Encore and Recovery (and some parts of Relapse) imo so he's a contender.
Ghostface Killah - Again, only mis-step he's taken imo were The Wizard of Poetry.
Ill Bill - Very strong contender. Can't name a "bad" album from him in the last decade. Alot of his best material was released in that time frame.
Immortal Technique - Great material but is too inconsistent. If he were to have dropped more material he may have had the title imo.
Jay-Z - my favorite Jay-Z material is from '01 - '07. After that he fell off.
Kanye - Two classic albums halfway thru the decade, one bangin album in '07 and one wack album that can't even be classified as hip hop in '08.
Killah Priest - Not a fan besides Heavy Mental so my opinion on him isn't really relevant.
Lil Wayne - He was good until the Carter III. After that he was wack so he's not a contender imo. His material from '03 - '06 was great though.
MF Doom - One of the strongest discographies of the bunch. One of the top contenders imo.
One Be Lo - Again, have yet to hear something bad from him. Another strong contender.
P.O.S. - Never got into him. Someone put me on cause I hear good things.
R.A. the Rugged Man - To my knowledge he dropped like one album last decade of new material. Legendary Classics was basically re-mastered old shit. Good shit though. Can't be a contender for me though for that reason. One album isn't enough I need more.
Royce da 5'9" - Only solo album of his I have is Street Hop. It's great but I can't say he was top of the decade until I hear more material from him.
Sean Price - Didn't drop new material until about '04-05 (to my knowledge) so I can't really say he's the best of the ENTIRE decade but I will say that he has had an amazing run since Donkey Sean Jr. One of my favorite emcees.
All that being said I think MF Doom takes it imo. Between him and One Be Lo.