All of the videos are high quality, so my comments are focused mostly on the content, not the quality.
The classic cinematic is the best overall because it largely focused on the classes rather than specific characters. This focused heavily on what character classes players can play are capable of, such as the warlock controlling the infernal, or the druid shape shifting.
The Burning Crusade had a similar theme focusing on the playable classes and even more heavily on the new races. While Illidan is narrating a bit of the video, he doesn't really get shown until the very end which allowed them more time to focus on what players get to play. They also showcase some of the non-playable creatures in this video (naga and murlocs in particular, and the playable races/classes make short work of the non-playable).
Wrath of the Lich King introduction focused mainly on Arthas. It no longer featured anything playable by the player. It was just the enemy you will be facing. The video itself was fine however it does leave the question open to someone without a background in World of Warcraft prior to it, "where do I fit in"?
Cataclysm went even more extreme than the Wrath of the Lich King introduction. Deathwing really is the only character represented at all. Not even his followers really, just him tearing up the world. Honestly the single best thing that came from the Cataclysm introduction was the launch stream done on Legendary where they made fun of it by doing the "pain... agony..." part and extended it by like three minutes.
Mists of Pandaria shows the strongest of the new race and new class making short work of a classless human and orc. I can't see players really identifying with any of the three characters in the cinematic because the human and orc are too generic and weak. Meanwhile the monk shown is the greatest monk. This is something to the effect of pitting Malfurion Stormrage against a city guard. The video is nice and all, but the problem goes back to "where do I fit in"? So I guess the question remains... "why do I fight?" Because I am not in the video.
"In anything, if you want to go from just a beginner to a pro, you need a montage." /w TankSpot WTB Montage for Raiders.