I think it's very elegant and beautiful. My preferred spelling is
Vivian, but it really depends on what fits best with the combo. To me
Vivienne and
Vivian have different feels.
Vivian is dark and magical, while
Vivienne is lighter and frillier.
Vivien kind of confuses me when I look at it in trying to get an impression of if because it's like a merging of the other two spellings.