Or Haskell if you want to go the FP route while CL or Clojure for the Lisp. Or python for dynamic (atleast more popular than Ruby which is more concentrated on Rails ecosystem).
I don't like Python, but I have to admit that it ticks most of the boxes of an ideal starter programming language, unlike CL, Clojure, other Lisps, Ruby, or C/C++.
Teaching marketable skills that are already popular and actively sought after may be an important aspect influencing the decision.