Much prefer teamspeak due to the wider range of options and what i find to be a more user friendly interface.  Love that you can make your own channels and the way phantoms work in TS3.  The symbols on the side are also a cool addition and make it easy to see who is who.  I find the voice quality to be slighly better than Ventrilo and have had no connection issues (except telstra hamsters dying but that is my end).

Love it.

Afterthought