I have Mechbunny, KVS and Smart Tube Pro.
My personal favorite is still Smart Tube Pro all these years later.
KVS is great, and their support is excellent, but there are so many options in the admin area it can be overwhelming. Also, templating KVS can take a long time to do. If you want to try out a different design, you have to replace the current templates or get a test.domain.com setup by kvs for development.
With Smart Tube Pro, if you want to test out multiple site designs, to work out which runs best it is no problem. Simply send traffic to the new template design
http://www . domain . com/?template=old or
http://www . domain . com/?template=new. Also, it is much easier to template than KVS. I have custom STP templates using just 14 template files for tube site.