In my testing the JavaScript version had a better "boot time" (it was able to begin showing results instantly) - and rendered better/faster for simple examples.

In my testing the JavaScript version had a better "boot time" (it was able to begin showing results instantly) - and rendered better/faster for simple examples. However, the Java Applets simply scale better. They can handle pretty much anything you throw at them. If you're just tackling simple stuff (pretty much anything that I demoed on the site) then Processing/Canvas is probably the way to go.