[xefyr]

Depends.

Do you know anyone already using any of these languages? The path to enlightenment is almost always more easily tread when you have someone hiking it with you.

If no, choose by documentation. What do you find the easiest read? I was first introduced to lisps via PG's "ANSI Common Lisp" -- great book. If scheme's your thing, SICP is the way to go. I haven't been following Arc and I'm not up to speed on Clojure, so I cannot comment on those tools.

I chose Common Lisp. Openmcl on my ppc and sbcl on x86. Your milage may very.

Best of luck!