Because it's my name. :)
No, really, I don't think there's anything inherently better about either one, but I certainly think
Catherine suits me better. I think the C looks softer and makes the name look more feminine and sweet. I think it's also a bit more formal and elegant. I prefer not to go by a NN (well, I
do kind of like
Kitty), and I think
Catherine is less likely to be presumptuously (lol) shortened to
Kate,
Katie, etc. (although the threat of
Cathy still looms . . . ).
Katherine works well if you are going to use
Kate,
Katie,
Kitty because it retains the K, but I still think I could claim
Kitty as a NN despite my spelling of
Catherine (and Citty just looks silly!). I am not one of those C/Katherines who tries to claim that
my spelling is the
correct spelling. I understand that there are several acceptable spellings of my name and I think each one has a little bit of a different feel.