On some level of thinking, I was also considering the IDEs for each.
The first IDE with a dialog editor I encountered was Eclipse, which was a pain at first (yeah, i'm new to Java still). I installed it the first time, expecting to create a JFrame and drag controls on to it. I wasn't able to do this, and checked through the menus looking for some sort of "dialog editor". I went back to the site, and after some research determined that I needed the "visual editor" plug-in. So, I downloaded and installed it (not trivial for unexperienced people, but easy if you are). Still didn't work. The "visual classes" were missing, and I consulted site help, which was outdated. Well, after getting a bit angry, I finally discovered that I was missing dependencies, which I downloaded, and I finally got it working the way I wanted. Much different experience from that of Visual Studio. Eclipse is a bit slow too, but Version 3.2 Milestone 4 seems faster (but it's "beta", and it has some annoying bugs). It's a really good thing I already knew about layout managers, or would have really been in for pain (drag button onto content pane of JFrame, and it takes up the entire frame and can't be resized, which is odd default behavior in my opinion).
I've never used NetBeans but i've heard very good things about it. I'll probably give it try, when I can get a better download speed from their site.
Btw, has anyone else checked out the new features for Mustang (jdk/jre6 aka 1.6.0)? "System tray" support, splash screens that load before the VM?, Reflection improvements, new API for working with the java compiler. A java.io.Console() static class, and some other goodies. I'm particularly looking forward to the Java Compiler API.
I hope Microsoft continues on their path with .NET (hey Microsoft, thanks for adding WAV support to the 2.0 framework, and not bothering with anything else). Their seeming abadonment/deprecation (in some ways, like a lack of documentation for directui.dll) of the native win32 DLL, or just disorganization in general, is giving people a reason to research alternatives. I'm not impressed by their 2005 IDE either (HTML editing still sucks, terrible CSS code output), and I find myself correcting IDEs that auto-generate code I don't like (and yeah, I "correct" Eclipse too).
Edit: Tried NetBeans. I still prefer Eclipse .