YouTube is great when it works, and sucky beyond belief when it stutters and buffers. Google's opened up its Google Video Quality report to Australians so you can see how well your ISP performs.
The Quality Report simply offers a guide to the typical performance of your ISP as calculated by Google, so if you're using a VPN consistently it won't give you the right figures. You can then compare those figures against other ISPs, again as determined by area, although it's not terribly region specific, lumping Sydney in as a single area, for example.
Google also offers up a set of tips to improve your video quality, covering the basics -- such as making sure that others aren't hogging all the bandwidth -- and the truly fundamental, such as restarting your computer and router.