C is the best because it is simple and very powerful (in terms of the programs it can generate, not how easy it is to write them). It is too low level for a lot of things though. C++ is unfortunately the best for some performance-intensive code if you can use it well and need the speed, because it is well supported, there actually are some useful features, and you have C. Unless it's numeric, then FORTRAN is the best because it's the fastest.
LISP is the best high level language if you don't care about ease of learning or available libraries or windows support (yeah, CLISP, but it has licensing issues and it is an interpreter. Also you could pay $1000 for a commercial version). And you want to use emacs. It was evolved over a long period of time (before it was standardized) and it's a big language so it probably has what you need and does it reasonably quick.
Lua is the best scripting language for a C/C++ app because it's clean, simple, portable, and fast.
Perl is the best language to use CPAN, and for text processing.
Haskell is the best language to use if you just want to play with clever ideas and don't want to write a real program (at least one that deals heavily with changing state or external libraries, which is most of them). Probably the best for writing a compiler or theorem prover or something.