Feedback on baby girls name, please!!

Kaleigh
I have two kids now, 9 1/2 year old boy, Cashe, and 6 year old girl, Anya. I have loved the name Ava and Stella for a long time. I decided Ava is a little too close to Anya and is too popular. 
Baby's middle name will be Kate (after a great grandmother). I recently came across a 3 year old Vivian/Vivienne, who they called Vivi! Now that name has really grown on me! Help me decide what is cuter or sounds better. Feel free to throw in other ideas as well! So these are the two names I'm debating. I can't decide on the spelling for the second one.  What do you think?? 
Stella Kate Gilson
Vivian/Vivienne Kate Gilson (nn Vivi)

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