I'm back from Netbeans World Tour from Poland so I'm totally unbiased :-). During the tour we discussed Eclipse RCP vs. Netbeans RCP again. Actually all of the comparisons I know right now are feature by feature comparisons, which are not very interesting for a real world project. Who cares about a slightly better help, or a different configuration of the menu system?. Both platforms are very comparable; Netbeans relies heavily on the ServiceLoader, which is part of JDK 1.6 and Eclipse RCP uses OSGI which is JSR-291 and will become indirectly a standard (via JSR-277). I read several comparisons, attended at JavaONE 2008 sessions, and all comparisons were so far somehow theoretic if not esoteric.
Because both platform have similar feature set and are both really mature (Netbeans RCP is older, whereby Eclipse RCP is more popular), a feature matrix is no more that interesting for choosing the right platform.
The key difference between both is the UI-Framework. Eclipse RCP is based on native SWT / JFace framework, whereby Netbeans is based on Swing. SWT started as an IDE-toolkit, and Swing was designed as application toolkit from the beginning. Swing isn't native, so that you can extend it, change its behavior in unlimited ways. SWT is more limited - some even trivial tasks can become interesting (in one project we spent an amazing amount of time to provide a vertical lable for a caption of a table). In the role of an architect I would always prefer Swing for UI development, because actually there are no limits. Swing is mature - actually too mature, it hadn't change for several years :-). I prefer Swing programming model too - but this is my personal opinion, in both camps developers can become slightly religious about this topic.
In my opinion SWT / JFace is rather a limitation, than an advantage for a business project. From strategic point of view Eclipse RCP could be more interesting because of countless already existing plugins and extensions. This makes Eclipse especially interesting for development / extension of already existing platforms like SAP, IBM etc. OSGI is hyped at the moment - this should be considered choosing between both of the platforms as well. On the other hand, Netbeans RCP is perfect for the migration of already existing Swing applications - which are countless as well. Since JDK 1.6 u7 and u10 Netbeans RCP has a huge advantage- it already exists on every JDK installation - as VisualVM. ...It is a Netbeans RCP application...