I have experience with the Eclipse RCP and would recommend it.
If you choose Eclipse RCP, defiantly get this book, it is invaluble when just starting out with the framework: http://www.amazon.com/Eclipse-Rich-Client-Platform-Applications/dp/0321334612
I can't say enough about the Eclipse RCP platform. I would recommend it for any Java desktop app development.
It's free, has great tutorials, and allows cross-platform development of rich desktop applications that use native OS windowing toolkit, meaning that your application will look native in any platform. It also has a clean API that stays out of your way, and makes deploying to any platform a piece of cake.
If your interested check out this book: http://www.amazon.com/Eclipse-Rich-Client-Platform-Applications/dp/0321334612
I have done quite a bit with an RCP application that made use of multiple plug-ins. This book helped me tremendously in all fronts: RCP framework and plug-in development:
The book walks you through the development of a IM chat client using RCP and plug-in development.
Also the eclipse site and IBM have some pretty good tutorials, here is one: http://www.ibm.com/developerworks/library/os-ecplug/
I agree with Thomas Owens on "Eclipse Rich Client Platform: Designing, Coding, and Packaging Java(TM) Applications" and would also add "Eclipse: Building Commercial-Quality Plug-ins" to the list of rather outdated but still somewhat useful books on Eclipse RCP. Even though the latter does not go much into the Rich Client Platform, it explains quite a lot about the Eclipse plug-in architecture that is useful knowledge for developers of RCP applications.
There has been a lot of improvements in the Eclipse RCP platform since the release of both of these books, so I really hope that there are new versions of these books coming out soon.
RCP has a bigger learning curve, but once you learn the basics the Eclipse IDE itself supports building RCP applications very well. I have only built a plugin for NetBeans (not build a full-fledged application), and the learning curve was lesser than for the RCP application. The book Eclipse Rich Client Platform: Designing, Coding, and Packaging Java(TM) Applications provides a detailed introduction to building RCP applications.
Pretty much any java, eclipse, netbeans swing books should to the trick.
1) FREE --- Thinking in Java (http://mindview.net/Books/TIJ/DownloadSites)
2) CORE java , vol 1 and 2
3) Swing hacks : http://www.amazon.com/Swing-Hacks-Tips-Tools-Killer/dp/0596009070
4) netbeans RCP : http://www.amazon.com/Rich-Client-Programming-Plugging-NetBeans/dp/B00132S6UU/ref=dp_kinw_strp_1
5) eclipse Rich client programming -- http://www.amazon.com/Eclipse-Rich-Client-Platform-Applications/dp/0321334612
Hope this helps.