Unlike some other users, the YouTube App works great on my iPad. But some of the longer videos sometimes stutter or stop to buffer, even though I am in Korea and the WiFi here is lightning fast.
However, I stumbled across a tweak that seems to really improve YouTube performance for me.
Connect your Wifi, and then go to Settings, Genera, Network and click the blue arrow for your WiFi connection. In the DNS setting, change the server setting to 18.104.22.168
This has totally eliminated all buffering for me. Like I said, YouTube was working fine for me, but this tweak made it even better, because now I can speed scrub through video clips in no time.
Hope this helps.