Two points for Eclipse
Mathias wrote about why he is switching to IDEA. From talking with IDEA users and watching demos at conferences, its obvious that IDEA has the polish and finish that Eclipse + web tools + duct tape doesn’t.
However, Eclipse has two key points going for it that keep me loyal: <ol><li>Eclipse has dominant market share. If you are doing consulting or contracting with clients who use WSAD or Eclipse, coming in with your own IDE is often not an option.</li><li>Plugins: RadRails, PHPEclipse, Ruby Dev Tools, and SpringIDE are without an equivalent in IDEA. Point #1 means that Eclipse will remain the leader in the plugin war. This will be key as experienced Java developers increasingly turn towards using non-Java languages, either as a wholesale replacement for selected apps or for bits and pieces while talking to core Java on the same JVM.</li></ol>