Okay this is hard because I often prefer 'different' outfits for them, a.k.a. Not the ones worn at the same time.
I think this is when I like them about the same though.

MalloMar , Which are your favorites for each of them individually?

Similar to MalloMar, it's kind of hard to choose which duo outfits I like the most when my favorite for both of them aren't in the same category.
1) Elsa's WW Anna's Coronation
2) Elsa's OFA /Anna's FF
3) Elsa's FF/ Anna's OFA
4) Elsa's Coronation /Anna's WW
I ultimately choose OFA because I guess this is the nicest combo. I didn't include Frozen 2 because I don't have many good images of those dresses.

Coronation dresses and Frozen Fever ones as well. The OFA's dresses are kinda plain for me. Frozen 2 one seems pretty good though.

The Frozen 2 outfits look great, too!
I no doubt prefer Elsa's frost dress to the coronation dress, but I also like Anna more in her winter getup. The Frozen Fever outfits are just okay. The OFA outfits are also okay; Elsa's dress is gorgeous, but I don't love how it looks on her.

want now!

best dress win

Looove these!

For Elsa her dark blue Christmas dress and for Anna her outfit from Frozen II.

It’s hard to choose because I don’t like some of Anna’s dresses as much as Elsa’s and I wasn’t too big a fan of the birthday special dresses. This is the only one where I love both of them

Since I was asked,
The dresses I prefer are actually pretty much the same ones LMH5113 does.
The Frozen 2 ones look a little plain, maybe future pictures will convince me otherwise.
Thy do have some nice dresses overall. :)

MalloMar, ok, thanks for your comment. I picked this option because this is my favorite dress Anna wears, and it is my favorite Frozen outfit overall. Although, I do prefer Elsa in her coronation dress. :)