I really like
Rowena, however, I hate the 'ween' sound because it reminds me of wiener. Also, I just find the 'wen' sound more attractive in this case. While I don't care for the way Rowenna looks, I do understand why some feel it would be necessary to avoid the 'ween' sound.
Ravenna doesn't appeal to me although again, I'd pronounce it with the 'wen' sound.