Java (used in, for example, OpenOffice and Azureus) != JavaScript (used in web-apps like gmail). Rather large difference, guys. Syntensity doesn't use Java, only JavaScript, Python and C++.
Well, either way, i seem to have gained more experience with cubescript in the same amount of time than I did when i tried JavaScript. As you can tell by my apps.
What did you try to do in javascript? And obviously, CubeScript is going to be easier to use, because it is made specifically for cube, and thus can be a way simpler. However, you won't be able to use cubescript anywhere else, as Obsidian mentioned, you won't be able to do as much with it, and web-integration would be nightmarish if you sticked with it. Using javascript, on the other hand, trains you in a language that is used all over the web, especially with HTML 5 coming out, and so learning it is a really useful skill to have. At least, as I see it.