I love them both but Whitney holds a special place in my heart. She was one of my starters and I'm super attached to her, she's probably my favorite out of of all my villagers.
It's a bit of a tough decision because purple is my favorite color and Diana has purple features, but I'd have to give it to Whitney. She just looks a bit cooler, and in general I prefer more realistic eyes instead of dots. I would also prefer to have a wolf instead of a deer if I were to acquire one.