What features of lisp are you looking forward to? If you just want to learn new concepts you want to keep things simple so could just stick with mit-scheme. You

What features of lisp are you looking forward to? If you just want to learn new concepts you want to keep things simple so could just stick with mit-scheme. You didn’t ask, but I would also learn SML (or Haskell) after you have learned some scheme because you will see the diff between type systems and get a lot of practice.