There aren't that many Lisp implementations, especially those that are considered to be mature and ready for production.

For Common Lisp, the open source ones are SBCL and Clozure CL, and the proprietary ones are Allegro CL and LispWorks.

For Scheme, there are Racket (PLT Scheme), Chicken Scheme, and Guile.

I'm quite certain that the majority of people who use Common Lisp and/or Scheme use one of the aforementioned implementations.