It well depends of the problem domain, sometimes productive programming is about best algorithms, for example if you develop a software playing chess you can't left it for later improvements.

I can add some of my experience (since I was 8 years old?), it works in my personal framework:

- Hybrid languages/technologies: for some solutions I need to use jython to develop in python + java libraries that you don't found in other languages (i.e: htmlunit).

- I have always an interactive console opened to test stuff while using an editor.Sometimes the language doesn't have a good interactive interpreter, my preference is using python (if using .net, then ironpython, if using java, the jython, etc).

- Since I do a lot of research for customers, research and proof of concept are first in the list to reduce the real risk in the project.

- When I need optimizacion/speed C/C++ is the language, but try to glue with python, ruby, COM, etc (SWIG is your friend).

- Sometimes debugging is the best option, sometimes focusing in the code and try to find the bugs in my head.

- Then I agree with Gabriel.