Finally a threat where I can praise Oda!
Let's start by comparing the main female protagonist
Nami
Here we can see that initially Nami was a modest girl with small titties but a good silhoutte.
Later on Nami tits grow(specially after timeskip) but her legs and ass remained shit.
So Oda art I would give Nami a 6 unlike Anime that made her hotter but with a unrealistic waist(creepy). Which has my 8.
Obs: I found a image where her waist is normal.
Orihime
Similar to Nami, Orihime also got thicker through the series but unlike Nami she remained well proportioned(normal waist) and didn't grow as much since Kubo always wanted Orihime to be above average girls from the series. Which has my 9(7 at the beginning).
Anime didn't had to do much fanservice with her so it is basically the same from manga.
Obs: I know Rukia is the main girl from Bleach but fuck flat chested girls.
So for main protagonists Kubo is ahead.
Now let's take a look on hottest women of each series.
One Piece Hottest Girl
Of course people have different opinion on who is the hottest girl of One Piece. I myself find Viola the one while Oda probably thinks it is Hancock or Shirahoshi. But is general consensus that Robin is among the top 3 of every list no matter what!
She easily has my 9.9(10 is for Viola) she simply rocks!
Bleach Hottest Girl
Just like One Piece, Bleach also has more than one candidate for top 1 girl but just like Robin, Rangiku is the one who are at everyones top 3 girl also receiving my 9.9(10 would be to Yoruichi).
But to talk about the mangaka with bst female characters designs I think we should also bring Kōhei Horikoshi from My Hero Academia. He has a large variety of female characters designs and most of them pretty hot. My favorite being Camie Utsushimi(10) while he main girl Ochako would be 6(8 at anime).