When comparing viva vs adapta-gtk-theme, the Slant community recommends adapta-gtk-theme for most people. In the question“What are the best Gnome Shell themes?” adapta-gtk-theme is ranked 2nd while viva is ranked 9th.
Ranked in these QuestionsQuestion Ranking
Pro Available in Blue and Orange themes
viva offers a blue and an orange them so users can pick how the theme looks.
Pro Follows the material design guidelines
Pro Most complete theme
It styles every nook and cranny of the OS UI, even the ugly Java apps look beautiful using this theme.
Pro Easy installation on Ubuntu
sudo add-apt-repository ppa:tista/adapta
sudo apt-get update
sudo apt-get install adapta-gtk-theme
Not only looks good, but really accelerates work on desktop.
Con Not finished
The them is not 100% finished yet, though the author does say he is working on it. Of course the latest commits can be seen on the github page with the last being from Sept. 2014.
Con No debian support