My favourite is Konqrr's original MKII vid. The combination of footage and presentation puts it tops for me.
Then there's MK Kompletions, which is close to top spot, for the same reasons as above. Plus it's extensive, and pretty sweet stuff considering it was done years ago now.
UMK3 Shattered is awesome, and I rank it highly, but behind Mortal Personality Disorder. That video kicks ass, I love the multiple characters linked into one combo chain (which is why you should look out for a video focusing on a certain "Deadliest Warrior" in the near future ;-))
Finally, I'll rate Max Damage into my top 5. However, they're all fantastic. It's almost criminal to leave out any of the Service Packs (especially 2 and 3,) but they've been surpassed!
So;
1) MKII Deconstructed
2) Mortal Kombat Kompletions
3) Mortal Personality Disorder
4) UMK3: Shattered
5) Maximum Damage
* This is all from memory, so I could be forgetting stuff.