When comparing viva vs Moka, the Slant community recommends Moka for most people. In the question“What are the best Gnome Shell themes?” Moka is ranked 3rd while viva is ranked 10th. The most important reason people chose Moka is:
Besides this Gnome Shell theme there are [multiple GTK and icon themes](http://mokaproject.com/) that match, giving the user a wide variety of themes to mix and match that still look great together.
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 Wide support
Besides this Gnome Shell theme there are multiple GTK and icon themes that match, giving the user a wide variety of themes to mix and match that still look great together.
Pro Several distro specific instruction to download
Moka offers suers easy to follow instructions to download including PPA's for Ubuntu based distros and Fedora specific instructions to install its repo.
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 Does not work on older version of Gnome Shell
Moka does not work on Ubuntu 12.04 nor will it work on Debian Wheezy as they both use old version of Gnome Shell.