Vim / Emacs
- Very fast/efficient code writing
- Low memory footprint
- Quick access to command line
- Infinite possibilities through scripting/plugins
- Never have to leave the keyboard
Eclipse
- Full-featured IDE for many languages
- Great refactoring support
All of them
- Cross-platform
- Feature rich
- Extensible through plugins
I typically find myself writing volumes of code through vim and performing debugging tasks through my IDE. Familiarity with the code base is certainly a factor, as an IDE is a great tool for jumping around and learning unfamiliar source code.