I think
Caitlin is nice, although its not my personal style. I only like this spelling.
I have been liking
Kathleen more and more lately, it used to sound really dated to me, but now I feel like it could be a charming alternative to
Caitlin.
I think
Caitlin's are usually called
Kate or
Katie, maybe
Kat. My niece
Caitlin (15) is
Kate.