Wrath > Cata >>>> MoP > BC > Vanilla
MoP, BC and Vanilla cinematics are pretty close together for me. Vanilla was just a showcase of a couple of iconic (mostly through that video :P) classes/races, Illidan's Cinematic was nice because I recognized a few characters in it, and MoP was nice because of the Pandaren Monk and Ally/Horde team up slapstick.
But nothing sent chills down my spine like the moment when Arthas created Sindragosa or Deathwing took off and started searing the planet. They are pretty close actually, but because my WotlK nostalgia is bigger than the Cata one I give the WotlK one the preference.