I don't know about best, because I don't listen to enough rap/hip-hop to make a definitive statement. But these are my favorites:
Outkast - Bombs Over Baghdad (I like pretty much anything Andre 3000 is associated with)
pretty much anything by Saul Williams
N.E.R.D. - Lapdance
Prince - Pussy Control (I really don't think Prince is considered rap or hip-hop, but he raps in this song)
Pastor Troy - Vice Versa
Yin Yang Twins are always fun
T.I. - Rubberband Man
Ludacris - Southern Fried Intro
Memphis Bleek - 'Round Here
"Rap is Crap" from the album "The ***** can't sing but he makes money with other ppl works anyway" by 2morrow I. Will B. Shoot. A classic.