I think NetBeans has a couple of advantages over Eclipse when it comes to building GUI applications.
- excellent GUI builder
- very good module system
- a mechanism for decoupling called lookup
- learning curve is not very steep as you stay in the Swing idiom and do not have to learn SWT
- good tutorials to get you started
- a useful set of wizards
- very good API to build explorers, editors, property sheets etc.
So far, whenever I build something which was against the NetBeans RCP idiom, it was fairly easy to refactor the code to apply what I had learned. There is also a book available in german and in english. Have a look here. I wrote a small review for it, which can be found at the end of the description, telling you what to expect.
If only Netbeans had better integration with modelling, such as Eclipse and EMF! Well, I guess we have to wait for Netbeans 23.1 M9 to see that.