Since Vocaloid song producers don't seem to get enough credit for their songs, I made a list of my favorite:

Wonderful Oppurtunity!
Popular songs: Remote Controller, Death Should Not Have Taken Thee!Influencer is Dead
(Only uses Rin and Len)

wowaka
Popular songs: Rolling Girl, World's End Dancehall, Unhappy Refrain

kikuo
Popular songs: Gomenne Gomenne, Aishite Aishite Aishite, Kimi Wa Dekinai Ko
(Morbid lyrics; mainly uses Miku)

Hitoshizuku-P
Popular songs: Soundless Voice, Corrupted Flower, Feathers Across the Seasons, Black Vow Alluring Secret
(She is known for producing tragic love story type songs)

rerulili
Popular songs: Knife, Sacred Spear Explosion Boy, Spinal Fluid Explosion Girl

samfree:
Popular Songs: Luka Luka Night Fever, Promise

Circus-P
Popular songs: Circus Monster, Insanity, Copycat
(Mostly uses Luka, Gumi, and Miku)

Nem
Popular songs: Dream Eating Monochrome Baku, Ah It's A Wonderful Cat's Life, First Love Academy, Superhero
(Mainly uses Len)

DECO*27
Popular songs: Ai Kotoba, Ghost Rule
(Mainly uses Miku)

ryo/supercell
Popular songs: World is Mine, Melt, Kocchi Muite Baby
(Mainly uses Miku)

Hachiouji-P
Popular songs: Sweet Devil, Kimagure Mercy
(Mainly uses Miku)

doriko
Popular songs: Romeo and Cinderella, Cat Food
(Mainly uses Miku)

40meterp
Popular songs: Love Trial, Karakuri Pierrot, Torinoko City
(Mainly uses Miku)

GuitarHeroPianoZero
Popular songs: Glass Wall, For The Better

Steampianist
Popular songs: Secrets of Wysteria, La Llorona
(Creepy AF)

PowaPowa-P
Popular songs: Please Give Me A Red Pen, Strobe Light

Giga-P and Reol
Popular songs: Childish War, Gigantic OTN
(Mainly uses Rin and Len)

koushirou
Popular songs: Lover's Onomatopoeia, Bye Bye Game
(Only uses Rin and Len)

Last Note
Popular songs: Akatsuki Arrival, Deadline Circus
(If you like rock music)

Kurousa-P
Popular songs: Senbonzakura, Cantarella

Polyphonic Branch
Popular songs: Tokyo Cyber Detective Brigade, 2Dimension Dream Fever

Neru-P
Popular songs: Lost One's Weeping, Abstract Nonsense, Tokyo Teddy Bear, Law Evading Rock

Maretu
Popular songs: Brain Revolution Girl, Mind Brand

Akuno-P
Popular songs: Daughter of Evil, Servant of Evil

Junky
Popular songs: Melancholy, Sweet Magic

Toraboruta
Popular songs: Kokoro, Soleil
(Mainly uses Rin)

minato
Popular songs: Magnet, SPICE!

Believe it or not, I typed this off the top of my head, so some of the information, spelling, etc. might be incorrect.