Has to be Birth by sleep.
It's such an incredible scene as it is, with gorgeous CG, choreography and cinematography.
But what really nails it, what really makes it the best, is Fate of the Unknown. Shimomura outdid herself with that track, which pairs with the scene beautifully and informs much of the tone and emotional weight throughout.
ASAS/[deep dive] is cool, but it's also incredibly frenetic and busy, incoherent with an absolute deluge of random information among snippets of action sequence. The track "Another Side" is buried underneath the myriad sound effects. It's a concept video, in the sense that it's an endless series of disparate concepts. Very exciting for fans and to this day a goldmine for theorycrafters, but not exactly a great video in its own right.
Yozora was really interesting an surprising, but it's very brief and without much substance other than those surprises. This one most of all (by virtue of being canonical and not a concept/preview) relies on the KH series and viewer's knowledge thereof to derive any sort of meaning or enjoyment from it.
Birth by sleep stands out as the one that, in my opinion, is uniquely capable of existing in a vacuum. You don't need to be a KH fan to enjoy Birth by sleep. It doesn't rely on you having knowledge of the series, it makes no grand reveals and it doesn't use familiar characters to tease at the future.
It excels at being a teaser for the new game, a reward for completionists and fans in general, and at being a damn good video in its own right.
Therefore, it's the best.