I am usually only targeting guile, mostly because of guix. Guile or chicken seems to be the most popular schemes, but Chez is a compelling choice when there are no external dependencies.
Hi John! I have always made the claim that racket (minus the #lang bit) is the natural continuation of r6rs. Delimited continuations, immutable pairs, continuation marks and such. They also chose, in my opinion, some more sane paths with regards to the dynamic environment and laziness.
If one could make a wish list it would be the suggestions in Marc's proposal in the chez issue tracker, immutable pairs, immutable strings, and RRB trees in the standard library. Like an opinionated love child racket and Clojure :)
Even though I am more.of an r6rs guy I have always applauded r7rs large. At the same time I am glad you put your own health first. That is always the most important. Apart from the r7rs process, your contributions to all SRFIs I have been following has been amazing.