Due to the preposterous number of Vocaloid songs out there, "best" in practice often means "personal favorites of the limited subset the person you are talking to has heard of". Vocaloid seems to follow Sturgeon's Law, as does everything else with low barriers to entry (like fanfiction), but fortunately, it doesn't take much time to check whether a given song is good, so hunting for hidden gems is a fairly fruitful activity as far as Vocaloid songs go. A useful site for this task is VocaDB

Endorsing Gwern's response below, here are five that I'd say are fairly decent.

Not is Destination The producer, Aerial Flow (that's his channel, by the way, poke around on it) is one of the best trance producers in the community, and there's quite a bit more stuff by him that I wanted to link but didn't.

Lost Memories A fairly nice Dark Append song that is tuned higher than the one you linked, but that I still suspect you may like. Not quite sure what to class it as.

Everlasting Love First song I listened to where I went "I like the vocal tuning on this one." Piano ballad.

Yumemidori Yes, it isn't Miku. Yes, it isn't electronic, it's guitar and drums. I'm still pretty enamored by it.

Idiolect Another popular techno song with the Dark Append.