I really like
Saoirse, but the prn is definitely not intuitve for American. Also love
Sorcha. I think both are evocative and lovely, but you would definitely have to live with the fact that people will struggle with the spelling and pronunciation.
Aoife is nice, too, but it is so close to the fairly popular
Eva, that I don't care for it as much.
Caoimhe doesn't do much for me.
I would definitely use
Saoirse or
Sorcha, though.