[pavelludiq]

Common Lisp, for it's maturity, stability(decades old code still runs on modern implementation) and remarkably good design considering it's a language designed by a committee. Almost all of it's problems or dusty corners that show their age can be worked around by libraries. Not to mention the quality of the spec is great. I really miss the attention to detail the common lisp hyperspec has when I have to read about some obscure corner of python for example.

I also spend some time with clojure around the time of v1.0-1.2 and quite liked it, but it's maturity level and the JVM made it less attractive in the long run.

I like scheme as well, but because of the spartan(to use a nice word) spec, If I actually want to get stuff done I'd have to chose just one implementation and it's associated libraries, rather than rely on portable code.