I really like
Johanna, personally. It's a soft and gentle name with a lot of history. I think it's feminine without being frilly. I don't think it's plain at all, and I especially love the opportunity for the nickname
Annie, which is one of my favorites.
I tend to think of it as a female form of
John rather than a mash-up of
Jo and
Anna, and I think that helps to make it more attractive.
I don't know any Joannas personally. My mom knows a few
Joannes, so middle-aged American women.