When comparing Guile vs Chez, the Slant community recommends Guile for most people. In the question“What are the best scheme implementations?” Guile is ranked 2nd while Chez is ranked 3rd. The most important reason people chose Guile is:
Guile makes it easy for users of your application to write extensions without needing to understand the plumbing of your program.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Easy to customize and extend applications
Guile makes it easy for users of your application to write extensions without needing to understand the plumbing of your program.
Pro GNU's official extension language
Chances are a system running enough GNU software will already have it installed.
Pro Excellent documentation
The documentation provides conceptual overviews, tutorials, and a detailed reference for all commands, functions, and operators.
Pro Fantastic interface to C, C++ in both directions, embedding guile in C/C++ and embedding C/C++ in guile
Pro High performance among Scheme implementations
Pro The only Scheme compiler to produce executables directly, without first compiling to C
Pro R6RS
Cons
Con Weak copyleft
LGPL
Con Limited third party lib and resources
Con Not available as a Debian package
Package chezscheme is available for Debian buster & sid, but not for stretch.