Out of those two, I voted for Diana. She's very beautiful, I love her white/purple/pink design. Whitney I find a bit plain (and I haven't seen the movie either), and I prefer deer villagers to wolf villagers.
I had Diana in my town once! I also had Whitney once upon a time. I didn't click with either of them so I don't have them now.
But I voted for Whitney because I clicked with her a little more then I did wth Diana. For some reason Diana got on my nerves as oon as she was in my town. Just annoyed me, no Idea why!
Both of their designs are adorable, so for me it would all depend of what you're looking for in town aesthetic!
If pastels and delicate things are what you're looking for, a deer character would suit that just fine, but if you want something a little more edgy (look-wise, not personality), I would go for Whitney.