I do love the mask, I wish that had stayed in for longer than a couple chaptesr of the manga. I also really like Sailor V's mask (though I suppose discarding it has some symbolic power. It's amusing to note that I can't recall Minako ever
throwing her mask, but people remember her doing that... but manga Usagi totally
does throw
her mask). The prototype designs in general for the Inners were interesting, in that I like how they were all more distinct and unique.
(Though some of them were a bit odd or ugly to me, like Jupiter's prototype design.)
I never posted properly because it's hard for me to decide. I actually like the wings on the Eternal form (though I got through all of Sailor Stars thinking those were constantly real wings, not decorative, because of the feathers in the transformation and the real feathery wings she uses later), and I kinda like the white boots too. Always thought the pink shoulders looked kind of funny and out of place with the rest of the scheme though, I call them her "bubble gum shoulders".
I'm sentimental for the original form from the first two seasons.
Princess Serenity is really cool. Any time the Princess Serenity or Prince Endymion forms show up, it's awesome, and they always liked to save that for the most dramatic and important moments of getting in tune with themselves to confront their biggest challenges. Plus any Silver Millennium flashback greatly intrigues me. (Also, this never happens in the story, but I think the Princess Serenity form would look amazing with the mask from the prototype design!)
Plain old Usagi is nice too, but at that point I'm not sure if I'm talking about costume design anymore because she wears lots of different things, though generally it's pretty cute.
The only thing I really like about the Crisis Make Up version of the super form is the really big long bow in the back. Bows are neat and enormous ones are cool.
I do actually like Zoisite's disguise
though that probably doesn't count. I especially like that he's able to wear bare legs over his pants and then drop them off like a rumpled suit. I also find it intriguing that it (sort of) got Zoisite a figuarts toy, and that they decided to use that form in the Sega Megadrive (Genesis) game
because they were lazy and that was easier than having proper sprites for him.