Oh that's such a hard question! I kind of agree with Kumiho. Harlem shake was hilarious the first couple I've seen but after a while they get old. Flash mobs will always be a classic.
Flash mobs, because all of the Harlem shake videos are kinda the same and flash mobs vary :-).
the harlem shake of course
Harlem Shake, hands down!
Con los terroristas :D