I guess... I'd say it was about equal. But Elsa is my favorite of the two.

Yeah. No doubt.

Honesty I prefer Elsa over Anna by a bit because of how damaged and pretty much more detailed of a character she is with her powers and design. BUT I hardly saw much of a change from her... Well till the end somewhat, by coming to amends with Anna. With Anna you really get to see her in her journey, how she comes to view Elsa, how she matures a bit, and discovering that maybe your first love isn't always your ever after.

I prefer Elsa over Anna but I think Anna is a way more well-developed

I don't think that Elsa is well-developed at all.

How did Anna develop? She didn't change at all. Except that she learned that she shouldn't marry a man she just met. While Elsa in the other hand became more confident and wasn't scared to be around people.

Both are equally developed, in my opinion.

At least she had SOME development.

I literally know nothing about Elsa other than she's Anna's sister, she has snow powers, she's the queen, and she's a fearful shut-in because of her terror of her powers. I don't even know if she's reserved and sophisticated by nature because we see her "put on a show" for other people, but once her composure crumbles and her secret's exposed, she flees in TERROR and the movie focuses on Anna. What kind of person is Elsa when she's not obsessing about her powers and/or her parents/sister aren't around? I have NO IDEA.

She has no identity outside of being "the snow queen" and being Anna's sister.

Elsa is no real development, she's not even really a character. Anna has at least some development.

Elsa could've had more development.