I've played around with at least half a dozen lisp dialects. Currently only Clojure and Common Lisp are good practical general purpose lisps(maybe Racket too, but I've only played with r5rs Scheme, so I don't know for sure). Both are excellent languages, both with their own strengths and weaknesses. After using Common Lisp for a while now, its my favorite language, and Clojure comes in as a very close second. IMHO these are the two BEST dynamically typed languages that are currently used in practice.

Choosing between the two could be hard, but my general advice is that if one prefers a more strict FP approach, Clojure is better, and if one prefers to have more choice over what paradigm to use when, a good multi-paradigm language like Common Lisp can make you happy. I happen to like the latter. Which reminds me, I have a lot of lisp hacking to do, enough HN for the evening.