CL is like the C++ of the Lisp world. It's standardized, multiparadigm, has a ton of functionality, fast, and built with large codebases in mind. It's also got a lot of cruft and because the standard is old it lacks certain things people expect, like networking and threads. Implementations usually provide these and compatibility libraries do a decent job of smoothing over implementation differences. Choose CL if you have a team, a large project, and you need speed.

Scheme was written for educational purposes. It's very minimal, and implementations aren't very compatible for anything outside the spec and the SRFIs (specs for optional functionality). I'd you choose a major implementation like Guile or Chicken however, there are tons of libraries available and it's very usable for small and medium-sized projects. It isn't known for its speed. Choose Scheme if you think like a computer scientist.

I've never used the others enough to comment, although I did enjoy playing around with Clojure since it's a functional language. I'd do more with it if it wasn't tied to Java and JavaScript. I keep telling myself to learn some Racket, but I never have the time.

Personally, I do most of my Lisp work in elisp, since my regular job isn't Lisp-based but I need to mangle text a lot. elisp is from the same tradition as CL so it's pretty similar.

Typical, asked for a tree and returns a flat list...