After trying TextMate, Eclipse, IntelliJ IDEA and Sublime, finally I decide to use emacs to be my final (maybe?!) editor. Although TextMate is the fastest & gorgeous one but unfortunately it's still weak in scala bundle.
I haven't used emacs since I left Yahoo! TW (2 years+), but there seems a magic between my fingers that I can perform most complex key bindings even I have forgot them, maybe it's a subliminal... :p
Add sbt plugin in your Plugins.sbt
addSbtPlugin("org.ensime" % "ensime-sbt-cmd" % "0.1.1")
Generate your project file
./sbt ensime generate, it will generate your ensime project file.
Open emacs & connect to ensime
M-x ensime and specify the .ensime file you generated, it may takes a moment for loading.
Check user manual and familiar with what you need in your daily coding...