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?

>>11
SBCL doesn't provide an interpreter.
False:

(defparameter *evaluator-mode* :compile
  #!+sb-doc
  "Toggle between different evaluator implementations. If set to :COMPILE,
an implementation of EVAL that calls the compiler will be used. If set
to :INTERPRET, an interpreter will be used.")

Shut up.
It's a widely known fact that most (Common) Lispers prefer public-domain, MIT, BSD, LLGPL to GPL. This is not an invitation to start a flame-war about licenses, merely a statement of facts (which you could find out by polling c.l.l, or merely looking at the licenses used by most CL libraries, GPL ones are a very small minority).