Common Lisp interpreter

I'm reading Land of Lisp and the guy uses CLISP (and CLISP specific extensions), so I'm using it for now. But I've heard good things about SBCL and others. Which one would you recommend? Should I stick with CLISP?

>>18
Interpreting is mostly useless, unless you have code that's heavily littered with eval calls, but we all know that's bad form (of the same type as fexprs), however SBCL's compiler would be slower than the interpreter in such cases.