Since it's an Italian name, my default pronunciation of Francesca is with the CH, because in Italian a C followed by an E would produce that sound.
On a side note, I did see once the variant Franchesca, which I imagine was used to prevent people from pronouncing the first C like an S; however, the "Ch" in Italian produces a hard-C, so looking at that spelling hurt my eyes.
***
Please rate my personal name lists:
www.behindthename.com/pnl/69381www.behindthename.com/pnl/69381/109399www.behindthename.com/pnl/69381/91835http://greens-end.myminicity.com/