This is the same question for older version of Scala, but they say that Eclipse plugin has been improved vastly. Is it the best IDE now? How do different Scala IDE compare t
It partly depends on your style of working, as all the options have strengths and weaknesses.
If you need refactoring across mixed java/scala projects, then IntelliJ is your only option.
If you want to do any work on the compiler or a compiler plugin, then Eclipse has the advantage of being able to launch a runtime workspace with a custom compiler build, including breakpoints. It also improved massively for the 2.8 Scala release.
Netbeans is a fine choice to go with if you're already very familiar with that platform, the costs of learning a new environment may well outweigh any benefits, and all three solutions are improving rapidly.