If you want to learn a LISP dialect just for fun and/or enlightenment, I would say you want either a Scheme (Guile or Racket) or Clojure.
Some people will argue that Clojure isn't a real LISP, which is fine. They're probably right. But it's an elegant and well-designed language that has a lot of the same features and feeling of a LISP/Scheme.
I know I could be burned alive for saying it, but Common Lisp is pretty ugly, IMO. It's "pragmatic" and has a bunch of libraries and functionality and whatnot, but it's not as fun or elegant as a minimal, pure, Scheme.
Some people will argue that Clojure isn't a real LISP, which is fine. They're probably right. But it's an elegant and well-designed language that has a lot of the same features and feeling of a LISP/Scheme.
I know I could be burned alive for saying it, but Common Lisp is pretty ugly, IMO. It's "pragmatic" and has a bunch of libraries and functionality and whatnot, but it's not as fun or elegant as a minimal, pure, Scheme.