For a long time I have been using Intellij IDEA and my last experience proved how accurate my decision was.
I had to use Eclipse due to obligations in a company. The feature I had developed was tested well and it was ready to be tested on server.
However; I had to spent a day to see it on server for a feature I had spent one day to develop. Problem was a "class not found" exception which I could not solve although debug it until to native binding of class loaders. The class was in related jar under web-inf lib folder; what was the problem? Perhaps it was an init / static block issue; but there were no clue...
After spending a day; I noticed that although the project I was working was a maven project and had been imported to eclipse via maven plugin; test folders were being included to build path when you execute publish/deploy on application server. Yes, for eclipse there is not such a concept called "test folders".
I was so happy to find it out; after spending a day on this meaningless error. Then; i recognized how nice IDEA organizes it; execute coverage reports; analysis etc. And you do not have to install a maven plug-in or any other svn/git etc. plugin, everything is already added for you and they work.
IDEA is really intelligent and I enjoy to work with it. I remember my first experience with IDEA. I had preferred Eclipse at the end of day; but as people keep suggesting it again and again; I gave it a chance again and now what I think is IDEA is the best java ide.
Other products of Intellij are great too: RubyMine for ruby/ror, Pycharm for python ide. There are not real opponents in these areas as far as I know.
Okay Eclipse is open source and free but Intellij really deserves what it asks for; and if you are a developer; it's not a big amount to think: It's great tool to do your job efficiently.