I've seen the gaelic word for fairy spelled several different ways. In addition to the two spellings you mention above, I tend to use the spelling of Sidhe. As far as I know, however, they are all pronounced the same, as in the phrase "Bean Sidhe", meaning fairy woman, which became the word "Banshee" I'm trying to think a bit, but I don't recall ever hearing it pronounced any other way regardless of spelling, just as 'shee'.
Poet and seeker of knowledgeMountain Legacy
-- Born in the isles, raised in Appalachia