I use Emacs with js2-mode for small to medium javascript projects.
For javascript projects with hundreds of modules stored in different files, nothing beats IntelliJ Idea. It parses all files in a project and allows you to jump from function call to function definition, from overriden method definition to the definition in parent class, etc.
I've tried Eclipse, Aptana, NetBeans, Komodo and others, and they aren't even close to Intellij Idea when it comes to javascript support.
On the other hand, such big projects in javascript are rare and usually emacs or any other editor is enough.
