When I was specifically learning and using Scheme I also settled on Chicken Scheme. For the following reasons:

1. It was very fast. Code written in it was comparable to the C code I was writing at the same time.

2. Very good C interop. Writing code to make use of C libraries was a near painless experience.

3. Very good collection of eggs (packages, think Rust's crates). I rarely needed to make use of (2).