This is mostly for corporate, assembly-line production type shops. For hacker-shops and startups: use what you know best first, then look around for something that does the job best and learn it on the side.

For me, I hack in a language that absorbs all other languages and development methodologies and fashions them in its own image. (Lisp hackers have the smug look on their face, like that playboy bachelor you see in the morning who is just itching to tell you about his "last night" story ;-)