There are so many terrible female character designs it's so hard to pick just one as the worst, pffft.
I guess I'd go with Fiore from SO5, though, as my pick for worst of the past decade. Cuz even if you covered up all.... that.... it's still a ridiculously busy design between the hair and the hat and the wings and the tail and good lord lol.
(fake edit: whoops, looks like I was beaten right as I was typing this up lol)
For best I'd definitely have to go with someone from Bloodborne or Sekiro. Crow, Lady Maria, and Lady Butterfly all have fantastic designs, it's hard to choose a best.
However, for more biased answers (cuz even tho I know these aren't objectively the worst and best, they're personal standouts for me)...
I'd give Cindy from FFXV the title of personal worst just because her design is so god damn jarring next to everyone else's and in context, it makes her feel like she just walked out of a porno instead. What makes it extra frustrating is that I actually like her character and think her design from the neck up is cute as heck, so not only is her appearance sexualized garbage but it's also a completely ruining waste of an otherwise great character. Pisses me off so badly lol.
Personal favorite will not be a popular opinion here and surprisingly also comes from FFXV, but... Aranea. I know she's got the heels and the skin showing, but there's something about her design coupled with her personality that is just so... aaa, bad ass frickin' cool! Especially with the mask on. She's like epic cosplay goals if I ever got in shape enough to confidently pull a midrift off. I love her.