Though my mind changes on this on an almost daily basis, I have to say that my two favorite dunks of all-time (ask me again tomorrow and I might throw in Kevin Johnson or Dr. J or 'Nique...) are MJ with a ferocious throw-down on Patrick Ewing-(http://www.youtube.com/watch?v=OmxJvWW5Ksw)
and Vince Carter's ridiculous dunk on poor Frederic Weis (http://www.youtube.com/watch?v=XMrPjl-927Q&feature=PlayList&p=DDBA5EDF63D7D09A&playnext=1&playnext_from=PL&index=15)
I love the "Oh no!" or something similar uttered by the Knicks defenders as Jordan slithers out of the double team in the corner and then absolutely posterizes Ewing.
As for the Vince Carter dunk, I remember seeing it live and being absolutely blown away, thinking that my eyes were deceiving me. I have since tried to intellectualize the dunk by trying to figure what his vertical leap was on that particular slam. Weis is 7'1", or 85 inches tall. Assuming that he was bent down a bit as Carter soared, "Vinsanity" (or at least his crotch) had to have been about 70-80 inches above the ground to clear Weis' head.
Mad, mad hops.
No amount of intellectualizing, however, will ever beat the chills and visceral reaction created as people around the world, me among them, sat and watched a man soar above another grown man, this one some 85 inches high, almost sit on his head, and throw the ball throw the hoop with a frightening and exhilarating amount of explosive force.