I also like
Francesca but dislike
Frances. I suppose the reason it that, although spelled similarly, they're not pronounced the same (fran-CHES-ka with a short A / fraan-SIS with a long A).
I think Cheska is a cute nickname, and definitely nicer than
Fran or
Franny. I The spelling on nicknames doesnn't really matter, since you don't have to write nicknames down that often but Chesca or Cesca makes sense...