As a professional - assuming you mean “which can I put on my resume to get a job working in that language” - probably (not necessarily!) none, or maybe Clojure.

As a hobbyist, probably all of them. It’s worth at least trying to go through SICP in Scheme (use Racket with the SICP language), it’s worth learning CL (use SBCL) to fully appreciate everything the Lisp world has to offer without compromises, it’s worth learning Clojure because it’s, frankly, a little bit cleaner and more elegant than CL in many respects.

Next week I will try to answer your question with a new post. Stay tuned!