SBCL or Clojure, depending on your problem domain and your experience. I would personally not use PLT/MzScheme or Arc for the type of projects I work on, but t

SBCL or Clojure, depending on your problem domain and your experience. I would personally not use PLT/MzScheme or Arc for the type of projects I work on, but there are obviously people who do use them in production settings. I think you could use either successfully, but I believe there are usually better tools available. Clojure is definitely a moving target, but the JVM/Java foundation buys you quite a bit (JVM clustering products, pre-existing libraries, ability to use existing talent,etc.) SBCL is very productive, especially if you're doing a "greenfield"-type project. We've used it quite a bit, and I would say you save lots of time by using it for prototypes and for certain types of projects - but you can also lose quite a bit of time dealing with the warts, as well. Some of the warts we encountered didn't appear until we were in a production setting and a few were rather expensive to correct. We ultimately opted for a commercial Lisp for most of our CL work. The SBCL team should be commended for their amazing work, though. I'm always interested in hearing about how others use Lisp for deployed apps, so please come back and post once you've made some headway.