I would like to think clojure, but am old enough not to get my hopes up about "a lisp" approaching the mainstream. So that means scala (self preservation?)
Funny, since I wrote my blog in clojure/compojure and found it easy going compared to Rails (which, to be fair, I had attempted to learn before having any real programming experience). That was my first experience with "a lisp", and it went well. Unfortunately, I think self-imposed cynicism about lisp is a big part of what keeps it from going mainstream.
EDIT: however, I respect that experiencing lisp not going mainstream for years would kill pretty much anyone's optimism :)