If well done, one editor, because it keeps things much simpler:
- When learning some new language, it's better not having to learn a completely new IDE
- For projects that mix languages, having to install and keep open as many IDEs is a real pain. And it is easier to configure a full recompilation/application start/refactoring if all of it is in the same IDE.
Of course, a good support for the languages you use is paramount.