Both Eclipse and NetBeans are very good IDEs, both more than adequate for professional
Java development.
I've been a long-time Eclipse user, but switched to NetBeans a few months back, mainly because NetBeans has very good built-in support for
Maven (it recognises Maven projects out-of-the-box and everything works smoothly). To work with Maven projects in Eclipse, you have to install a plug-in and it doesn't work as well as with NetBeans.
Last year I've done a webapp with a lot of HTML and JavaScript using Eclipse, and had a lot of trouble with Eclipse, it sometimes reported bogus error messages in the JavaScript source code and sometimes for unknown reasons the IDE seemed to lock up for a few minutes while working on JavaScript code. In NetBeans, the support for JavaScript seems much better and I don't have those problems.
NetBeans does seem to use more memory than Eclipse, but RAM is cheap and if you have 2 GB or more it's not a problem.
I prefer NetBeans now, but you really have to just try them both out yourself and see what works best for you.
Besides Eclipse and NetBeans there's
IntelliJ IDEA, which is not free, but there is a free community edition. I've never used it for more than small toy programs, but I know some people who do and they like it a lot.
@David: Yes, older versions of NetBeans (older than 6.0) were not that great, but NetBeans 6.0 and newer are really good and have surpassed Eclipse in many areas (in my opinion).