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?

>>1
CLISP aims to be an efficient interpreter, while most other implementations are compilers (while also providing an interpreter). I would suggest trying out SBCL and ClozureCL from the public-domain and LLGPL ones (CLISP is LGPL), they are much faster as far as the generated code is concerned, and have fairly interesting features which CLISP doesn't (but CLISP does have some nice features too, such as arbitrary precision floats).