Interesting question, I've never stopped to wonder "How useful this video would be to a newcomer?". After all, MA's are merely just flashy stuff and definitely not a top priority thingie to learn IMO.
Frostbyte PUG displays various position and teamplay aspects of Leejunz, both are quite important.
Flagplay clip shows how to delay enemy cap/EGrab, but Bucha's appearance was a fluke so I don't think it's "educational" in that regard.
So yeah, if I'd have to pick helpful/useful video I'd definitely pick PUG video. As for favourite MA/flashy stuff video, I'd have to say "Harmony" if I'm limited to my own videos only.