I wouldn't use Common Lisp. I think it's quite archaic at this point.

Racket is, to my mind, the most interesting Lisp variant that's actively developed. The macro system / build-your-own-language facilities are like nothing else I'm aware of. This is worth learning about, because it's genuinely something that other languages don't offer. A lot of the rest of the ideas in the Lisp-family can now be found in other languages.