[lukev]

Depends on what you want to use it for.

If you want to create powerful, intricate production apps, you're probably better off with CL. It's got better libraries, a bigger community, and more history.

If, on the other hand, you're interested in learning Lisp for the purity, the "aha" moments, and to become a better programmer, I'd have to recommend Scheme. It's a lot simpler, more self-consistent, with an order of magnitude less confusing bits and "gotchas". But it's still every bit as good at showing why Lisp is awesome.

And, of course, I must mention Clojure, which aside from the JVM cruft is much "cleaner" than CL, but just as powerful and ready for production use. It's also even more intensely focused on functional programming than Scheme OR CL.