Favorite Season: Stars
I don't know why, I think it's because the first arc is so excellent? The one with Nehellenia's return. And even after that, it's just a solid season overall. I enjoyed the introduction of the Starlights, Usagi having someone else vie for her attention and how despite not having seen or heard from Mamoru since he left she remained loyal to him throughout. I have a lot of feelings about Usagi/Seiya/Mamoru. Also, CHIBI CHIBI, aka the cutest character ever.
I think the victim of the week formula didn't really work for this season because Galaxia was supposed to know the senshi's star seeds are the ones she's looking for, and yet despite the senshi showing up in each battle, nobody ever bothered going after them. That part didn't make sense.
S comes a close second because it's an excellent season with excellent villains and the introduction of Haruka/Michiru, so how could it not be awesome. Also, best final battle ever; those were really strong scenes even if it was ironically the only time Usagi didn't assume Serenity form. It was the most powerful emotionally IMO.
Least Favorite Season: SuperS
I won't lie; SuperS is the most visually pretty season. When I make graphics, I love making stuff from SuperS. But that's all it is; a pretty thing on the outside. Because the storyline is a mess and confusing, and Pegasus is everywhere and the most powerful thing in existence apparently, and the senshi and Usagi feel useless and Chibiusa doesn't even have a legit attack. I don't really care about the romance either, and I guess Chibiusa was always pretty low on my list of favorite characters anyway, so I don't really care for her taking the spotlight. This season just feels so unbalanced compared to the others, like the girls taking the backseat and that just doesn't feel right somehow.