I'm using Eclipse and plan to continue using it because that's what I know.
I feel that NetBeans is gaining momentum. I believe that Sun abondoned forte/SunOne and is now using NetBeans and teaching NetBeans in their online tutorials. Also, NetBeans has a visual Swing designer if you need it. Also, there is now an upgrade path from the simple BlueJ IDE which is a simple IDE used in education. Now, BlueJ has an upgrade path to NetBeans. (I would only recommend BlueJ for programming students that don't know anything about Java.)
I'm sticking with Eclipse, but I'm keeping my eye on NetBeans, I might just switch someday.
My Favourite IDE is Eclipse. Also I am more familiar with it. Lots of plugins are available for it. JBoss plugin for J2EE development, MyClipse from J2EE at a nomonal price, Apache Commons plugin etc. Has been there for while.
The preference for an IDE is highly subjective. While it can be instructive to hear why other people like or dislike a particular one, it's unlikely that you'll find the one that fits your development style best without testing all of them. It's a bit like the vi-vs.-emacs debates of yore.
if you haven't worked with any IDE it is worth to do a kind of evaluation (preferences in team, using sun libs/frameworks only etc.). but if your already used to one IDE think hard whether it is worth to switch.
for instance me: i am using eclipse for some time and am amazed and very content with it. switching now to another IDE would take some time: shortcuts, way of project organization, plugin alternatives, version-control issue (hence eclipse uses .project file), etc..
so before i cannot really see unique selling points in switching my IDE i rather go to invest this time to explore other areas to boost up my productivity (learning groovy, testability, refactoring etc.).
The only IDE that I would consider as an alternative to Eclipse is IntelliJ IDEA.
The soul is dyed the color of its thoughts. Think only on those things that are in line with your principles and can bear the light of day. The content of your character is your choice. Day by day, what you do is who you become. Your integrity is your destiny - it is the light that guides your way. - Heraclitus
The IDE I hate is whichever one I'm currently using; The IDE I love is the one I used previously.
I think the point about learning shortcuts etc should be amplified: it is very important to learn as much as you can about your given IDE.
I have written a blog entry which compares an IDE to a city: there are neighborhoods and little "hotspots" that you may not know, even if they are right in front of your face. For a given IDE, find the user community and find out their tricks. It can be stunning:
ps. The big 3 are, of course, Idea, Eclipse and Netbeans. I use Idea because my project uses it and pays for it. Eclipse is fantastic and has 90% of the features for free. I haven't used Netbeans but it seems to be gaining traction.