For me the most important difference is Lisp-1 vs Lisp-2. I had tried my hand at Common Lisp a couple of times before trying Scheme. The latter immediately felt

For me the most important difference is Lisp-1 vs Lisp-2. I had tried my hand at Common Lisp a couple of times before trying Scheme. The latter immediately felt "cleaner" than CL. My favourite implementation is Gambit Scheme and I have currently stumbled upon Gerbil (cons.io), a dialect built on top of Gambit. It's just fun to work with.