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
The officially endorsed and supported (by Typesafe) for Scala 2.9 is Eclipse. The current version is far superior to prior versions and includes a context-aware REPL, full-featured debugger, and even the ability to debug REPL statements. I think this question needs to be updated and the answers revisited.
For the moment, Scala Plugin in IntelliJ IDEA is the best. It handles Scala 2.8 well. IntelliJ IDEA Community Edition is now free and open source (and works with Scala), so I can't see any reason for not using it.
The plugin is still somewhat buggy (many "false negatives", i.e. the code without red underscores may not compile successfully; but almost no "false positives"), but perfectly usable. The best thing is that you can use IDEA's excellent debugger with Scala (not without some issues, but it actually works!).
FSC (Fast Scala Compiler) is also supported in latest builds. A huge time-saver.
The plugin development team is quite responsive. Some of the guys work directly in JetBrains and possess intimate knowledge about IDEA platform, so the development progresses fast.
try IDEAX the latest community edition of Intellij IDEA (version 10), it has improved scala plugin which has faster code compilation and exceution in addition to that it has Maven3 and SBT support with which we can develop Lift applications.
I haven't tried netbeans scala plugin yet, but I find that Intellij IDEA plugin is at any way much better a scala ide than the Scala eclipse plugin, which is sooooo slow that drives me crazy. Though swing applications don't work well with my tiling window manager.