Although I like the Three Lights'/Starlights' songs, and I love Seiya and Usagi's relationship, I didn't really like the other two Starlights very much. They came off as way too unnecessarily jerk-like in the Stars anime. I don't know if I could say they're exactly my least favorite though.

I find it amusing I've never posted here. 

Anyway:

90s Anime: 
*Classic:  Mars (She was always so unnecessarily mean to Usagi.)
*R:  Chibiusa, hands down. Especially her DiC Dub self. 
*Super-SuperS: Usagi.  I hated that her development was nerfed in favor of developing Chibiusa and them not being able to develop both the girls at the same time. I get she was childish and that was part of her charm, but sometimes the Anime leaned too heavy on that and forget she was a teenager and not a ten year old. Or that Chibiusa *is* a nine/ten year old and not a teenager.
*Stars:  StarFighter. It's mostly because I didn't care for the pushiness on Usagi. It vaguely gave me creep vibes in a way.

PGSM: Sometimes it's Sailor Luna even though I know it's the 'Cute kid' appeal, I felt she was occasionally..not needed. <<;

My least favorite soldiers are Sailor Uranus and Sailor Neptune because I don't like how they treat Usagi and the Inner Sailor Soldiers, plus I don't like their mean personalities either.

Sailor Jupiter for me, even though I remember how excited I was after watching her introduction episode when I first watched Sailor Moon when I was younger, and how cool she seemed, I don’t like her at all these days. I mean, she’s very boring to me, she doesn’t have much of a personality for me or characterisation, she’s just the tough, physically strong girl with a softer side, as well... I don’t know, she seems very plain and ordinary to me, when all the other Senshi stick out in one way or another... She has some serious moments during which I like her, but eh, it’s just something momentary.