Vim is my preferred editor, and I code Scala for a living, but I use IDEA for it. The main reasons are:

- The ability to safely rename identifiers.

- The confidence that the "Find usages" tool gives on a large code base (search just doesn't cut it).

- Immediate, contextual syntax error information.

- Excellent auto-complete.

- Quickly navigate to declaration.

- Syntax-aware indentation.

I usually have an sbt session open that is either running unit tests or running a Play Framework server (with auto-reload).