1.) The Twelve Kingdoms
When I watched it years and years ago it was the first time an anime blew me away with its character development and it will always have a special place in my heart.
Youko's growth is wonderful.
And I actually didn't realize how good the development of the characters were in Anohana until recently, because it happens so seamlessly.
But then, in preparation for the dub's release, I went back and rewatched the first episode, and realized just how good they were. I honestly want more episodes!
The series felt so short and I didn't feel like I got to fully understand the characters.
3.) My Hero Academia
It was incredible watching Izuku grow from a very insecure guy to the madman that he has become was captivating. Then there is Todoroki, who has good character development as well, and if the anime keeps adapting the manga I can say that many more get developments that will rock the story to its core.
Avatar the Last Airbender
Avatar the Last Airbender is on the line between anime and western animation but I think it has some of the absolute best an animated series has to offer. No matter what you look for in a series you will find it in ALA and this includes character development.