@roka @awg "multiple" is sort of an understatement. It feels like the only language that has more implementations is !forth . :-)

Many people like #racket, as it has an IDE that is very helpful to newcomers. #Chez is performant and complete. I quite like #guile as it's GNU, used for #guix and has some intriguing new async stuff I'd like to play with.

A decade ago when I did #SICP in uni, the course recommended Racket (then Dr Scheme) or MIT Scheme, but I used Guile because it had a very POSIX-y and familiar command line and I wrote my lab exercises with Makefiles running the tests.

Back then I also had a look at #gauche (also very script-y and POSIX-y) and #scheme48, which integrates well with SMILE in emacs. These days there's #geiser for guile, which is likely to be the best emacs+Scheme interactive mode out there.

As far as I'm concerned, https://wingolog.org/archives/2013/01/07/an-opinionated-guide-to-scheme-implementations is the canonical "which scheme?" page.