I like
Caitlin, but
Kaitlyn doesn't look as nice to me. Plus that's a more common way to spell it, in case that matters to you. You could still spell
Katie that way though, although I personally think it would be fine to spell it Caity or Caitie (although she'd have to spell it to people...). What about just
Cait or
Cate? I have a particular fondness for
Cait which may or may not be related to a video game. :)