The best developed, yes. That isn’t saying a lot really, but her character is genuinely interesting and her running dark humor/kawaii gag is actually the funniest in the crew. She is the one I would choose to be friends with if I had a choice, without question. Robin and Zoro deserve a Shakki Rayleigh situation in the end for sure.
Other girls are very good also though, although they play smaller roles, while many of the women are either sexualized or a goofy gimmick appearance. There are solid supporting actresses like Monet, Baby 5, Kureha, Dadan, Portgas Rouge, Kuina, and Ulti, but I can’t imagine any of these being well done as a character for 1100 chapters. Many people, by the way, most actually, do not appreciate how difficult it is to maintain an interesting character arc over such a long period of time.
Oda is only really good at writing women when he commits a very short period of time to their story. Robin has been the one exception, as Nami still has not had a significant personally payoff outside of Romance Dawn. I do appreciate that the characters we met first have the longest character arcs as her personal story and ambitions still have a good way to go to hit a true EoS high, like Zoro’s.
However, I’m going with a pocket pick Vivi as the actual best girl by the end of the series. She has to earn her place.