Sunset seems like the fair kind of rival. The one that shows up occasionally to introduce some new mechanic or provide training for the player and such, all with challenging but fair battles.
 
 
Trixie is the one that shows up more as comedy relief, but still provide some challenge, until at one point towards the end, she suddenly becomes extremely powerful and kicks the player’s ass.
 
 
Starlight is the kind of rival that doesn’t show up until towards the middle of the game and doesn’t start out as a rival, but eventually becomes hostile. Her battles are extremely difficult and has a puzzle element to it to trip up the player, even though it’s all just mechanics we’ve seen before.

Delightful

Pokemon Trainer Twilight vs Rivals Sunset,Trixie,and Starlight

@Background Pony #730A  
And Moondancer is the Gen V rivals. Probably the least antagonistic Anti-Twilight.

Sunset is the Silver equivalent. Initially angry and rebelious. Trixie is the Blue/Gary one. Rude showoffs with large egos. Leaving Starlight as the N counterpart. Both are well intioned extremist part of cult like group with noble ideals, but construe methods. SciTwi can be the Wally counterpart. Meek nobodies that later become strong contenders.

I could see Sunset as Team Valor and Trixie as Team Mystic. Starlight though…she would be more of the Psychic/Ghost type.
 
Team Instinct would be either Lightning Dust, Spitfire or RD.

These three belong together. The magical trio deserve their own spinnoff.

Love them <3