I was in the exact situation two days ago. "Okay, time to start a new project. Okay let's see what options I have.. Maybe about 32 is a good approximation"
I love learning new languages, studying different construct, different concepts. I get so much from studying or overviewing a language I might never use to actually write code with.
I also like my side project being spaces where I can affort to try different 'exotic' things.
So I started surfing, got to CoffeeScript, NodeJs or CoffeeScript and ruby (my last project was in AngularJS (javascript, no coffee) on top of Sinatra (Ruby). Loved it. Most recommand it.) Then it started being more Esoteric : Nemerle, Dart, factor (really interesting!! most recommand to at least check it out : <a href="http://factorcode.org/littledan/dls.pdf" rel="nofollow">http://factorcode.org/littledan/dls.pdf</a>), etc. But at one point (I was in a bus), it became clear. Clojure is the solution. Didn't know much about it, couple of really interesting article had made me keep a mental note on it. So I started digging into. Found love.
- Efficient Macros (way cleaner than Common Lisp)
- Incredible data-structures (Not just an other Lisp)
- Active and growing Community
- Can be purely functional
- Walk-in documentation (Rich Hickey is made to explain how great things he does are. I mean reading is doc is like an all-around course on developper's best practices)
- Full application in one language (Clojure and ClojureScript count as one. Heh.)
- It's made by Rich Hickey. (Just joking.. Ha.)
- Supports Concurrency out of the box.<p>It won over CoffeeScript and NodeJS.. mostly because I already knew Javascript too well. Didn't felt I would get that "deeper understanding", as you mention, I was searching for.
It won over CoffeeScript and Ruby (I didn't do that much ruby at all, though I love every line I've written in it).. Because.. well it's a Lisp! Deeper understanding of Lisp is a no-choice toward skills I'm seeking to acquire (Out-lined, partially, in On-Lisp, pg).<p>So there I am, studying Clojure and sharing my exciting discoveries. Hope the list you've given wasn't the exclusive list of language you want to use. I would vote Clojure anyway.