My cousin and my entire family go by the one that rhymes with the American pronounciation of Hannah and Anna (shaa-na), but i have known people of either middle eastern or Asian decent whose names rhyme with the Scandanavian pronounciation of Anna or Ana (shah-na). I have known one woman who pronounced it like it was spelled Shawna but i think that was an adult preference and not what her parents had in mind. Just a guess though.
So i guess it would depend if you want to draw the etymology back to Sian, or to whatever other eastern source my friends' parents had in mind. (E.g. i see that Hindi contains the word shana = hemp).