I'm definitely gonna have to say Timbaland for cus of creativity and longevity over a period of time.
Close second. It took them a while to grow on me (didn't like them for the longest time) but i'm gonna have to say the Neptunes... the stuff they make for people in their click is crazy... Lil Suzy by Kelis is crazy. She wants to Move was bananas to me (the use the same chord progressions all the time... but i'll let them slide... sh!t still sounds hot).
Andre 3000 and Soulaquarians get honorable mentions just cuz they make stuff thats different.
(for those who don't know SoulAquarians consist of Questlove, James Poyser (<--this cat is SICK!!!), and Jaydee (to the Ummah... not Jermaine Dupri).