I'd choose
Viviana, simply because it's more feminine.
Vivian - ok, this spelling gives off a unisex or masculine vibe to me though. I prefer
Vivienne for a girl.
Viviana - feminine, has the same sort of vibe as
Liliana and other -ana names. Refreshing, beautiful and full of life. I like the nicknames
Vivi, Vee or
Ana.