I haven't been able to decide on these names, so here's a poll for them.
Violetta for me!
I picked Violetta but I say it different than Violet. I say Violette and Violetta as vee-oh-lett(A) and Violet like the color.
Of course, it depends on the surname but here are my ratings as per my own preference.
They're all lovely, but Violet's less interesting and more overused than the other two options. I gave Violetta a slight edge over Violette, but it depends on the mn and surname.