Kalla

Though usually I'm not so keen on "variant spellings," the spelling Kalla reflects the original Greek word from which it derives: kallos. I am torn between Calla and Kalla as to which spelling I prefer.

I think this is a beautiful name, personally I would use it as a nickname for Kallista. I prefer the k to to the c because it makes it feel more Greek to me, also it's closer to kallos with the k so it seems more original.

It's a very nice name, but it looks prettier and more sophisticated with a 'c'.