They all have their ups and downs.
Team Speak has a larger userbase, is more complicated to setup and the program has more features (eg file transfers etc). But the voice encoding can't achieve that high quality and latency wise it is pretty average.
Mumble is easy to setup and the voice encoding is great and very flexible, hardly any latency. It doesn't have many features or addons are very annoying/hard to setup, also some people have been having trouble connecting and or being able to use their mic with it.
I haven't really tried Ventrilo but its quite old, offers a middle ground in terms of quality. Unsure of the rest as I never really bothered with it.