Hi Marcus,
Volla OS is basically a no-spy, no-tracking Android without Google and without Google Services (on which several non-Google apps depend).
Ubuntu Touch is a Linux based Operating System that has nothing to do with Android. The number of available applications is limited, while Volla OS allows you to use most Android apps. Both Ubuntu Touch and Volla OS come with Software Centers which make it very easy to install programs.
This guy has compared Volla OS an Ubuntu Touch:
https://www.youtube.com/watch?v=HaSzGMXqPc0
https://www.youtube.com/watch?v=neG2Z21epLI
I find him too critical, especially when it comes to Ubuntu Touch (which I like), but he's competent and thoroughly reviews both Operating systems.