It depends on what you need to be doing as a developer.
Java Studio Creator is meant for developers that need to develop a GUI on top of existing databases, web services, EJB, etc. It does not allow you to create Web Services, or EJB's, or even Databases for that matter (yes I know there are ways to do it in Creator but it's not designed to create databases).
Java Studio Creator provides almost all of the plumbing hooked up for you. App Server, Database software, etc. are already included and installed with the product.
Now, Visual Web Pack has been released into the Netbeans community to introduce the folks that are actually doing the creation of those Web Services, EJBs, etc. to the same ease of building JSF based GUI's for those projects.
There are a lot of things that can not be done in VWP, at this time, that can be done in Creator today.
For a history of how Sun Java Studio Creator evolves into Visual Web in NetBeans, see Winston Prakash's Weblog. The blog has been expanded to an article Using Sun Java Studio Creator 2 IDE or Visual Web Pack for NetBeans 5.5, and provides the starting point for the Creator Forum topic Sun Java Studio Creator or Visual Web Pack?.