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?

>>16
To be fair, most people don't actually use SBCL's interpreter much(eval compiles by default), but it is there.