Catherine was the most common spelling in
America for decades. When I named my dd, I looked to see which was the more common spelling because I didn't want her to have it misspelled her entire life. At that point,
Katherine was the most common spelling and is to this day. After the popularity of the royal wedding,
Catherine may very well pull out ahead once more.
For a fn, I prefer
Katherine because it's closest to the original Greek,
Aikaterine, and because I love the nn
Kate with this spelling only (no Cates for me).
Having said that, I love the
Catherine spelling as a mn. It just looks better in the middle, to my way of thinking. I'm sure there are exceptions, of course (
Mary Katherine), but for the most part, I like
Catherine.
BTW, I read somewhere online several years ago that C/Katherine is the only female name to be in the top 50 for the last 50 consecutive years. Seems to me that several others should join it (
Elizabeth, Sara/h). Perhaps the site was going by spellings only.