Scheme is not a single alternative. Racket [0] is a Scheme, which can be compared to things like Python or Ruby. There are other implementations, which should be used for different uses. For example, Chibi Scheme [1] is a nice alternative to Lua, but not to Python or Ruby.
Given your other two Lisps, I rather make this list:
I think Chicken[1] is a very attractive Scheme alternative. It's full-featured, fast, compiles down to C, has a very nice library (egg) system, and a relatively large and active user community (as far as Schemes go).
Given your other two Lisps, I rather make this list:
* Common Lisp (which implementation?)
* Racket
* Clojure
[0] http://racket-lang.org/ [1] http://synthcode.com/wiki/chibi-scheme