my all-time favourite:
1)Meltdown by Kagamine Rin <---- unique lyrics, and fun to sing along!
2)Paradichlorobenzene/Antichlorobenzene by Kagamine Len/Rin <--- catchy, brain washing song XD
3)From Y to Y by Hatsune Miku (although I like the utaite ver.) <--- soft melody and sad lyrics
some songs by composer niki who uses Lily for e.g : Jitter Doll <--- great for karaoke, the music arrangement is good, I listen to kradness ver. of this
and also by niki, WAVE <--- dance to the beat, go check out dance cover of this song, I listen to KanzentaiCell (Kanseru/ Cancel) ver. of this
Leia and If, both by Megurine Luka, coz they both are rock song
Miracle Painting by Hatsune Miku, this song is jazz
My preference for songs is quite wide. I also listen to some songs mentioned in previous posts, although my Vocaloid song collection is only 1GB
compared to Oreiora from Australia who has +50GB collection!