>What's the most popular Lisp in use today?
At least if based in 2016 GitHub popularity:
http://sogrady-media.redmonk.com/sogrady/files/2016/07/lang....
#1 Emacs Lisp
#2 Common Lisp
#3 Scheme
#4 Racket
Unless you consider Clojure a Lisp (yes it is, and no, it isn't...), in which case #1 would be Clojure, and then the others listed above.