Each has its benefits, depending on location.
YouTube: YouTube is probably the more populated site rather than google video, and you can find just about anything on it, yet there are many annoying comments and things in videos that can disrupt performance.
Google Video: Not bad, can search through YouTube videos also, and can be good location wise. For example at the moment I'm in China, which filters YouTube with "The Great Firewall of China", yet i still have access to google video.
However I would still choose YouTube over.