Tough one! I love both
Theodora and
Dorothea, please don't make me choose! I think they're both lovely, beautiful, exotic, very uncommon as well. That said, I do prefer
Dorothy to
Dorothea.
I have to say that
Dorothea has better nn's than
Theodora, I'm not a fan of
Dora, so
Theo or
Thea would be nice. For
Dorothea, there are awesome nn's -
Dot,
Dottie,
Dolly, etc.