It's decent, but you have a lot of alternatives.
Besides SBCL, you might want want to look at ClozureCL, ECL and maybe CLISP or ABCL. If you don't mind commercial ones, there's also AllegroCL and Lisp-Works, and some OS-specific ones such as Scieneer CL and Corman CL.
I mostly just use SBCL and ClozureCL, but others are fine too depending on what you needs are.
>>3
ABCL