I ususally say jo-HANN-a. I like that, cause it's closer to the proper European pronounciation. Pronouncing
Johanna as jo-ANN-a sounds kind of Americanized. (Ironically, I am American.)
Johannah would make the jo-HANN-a pronunciation more likely, definitely.
Joana would probably be pronounced like
Joanna, but technically it's a Portuguese name, and probably sounds different in Portuguese.
I like
Johanna and
Joanna.
Joana is okay. Don't like Johannah - that sounds overdone.