It depends on how many external libraries you need. We considered both Clojure and Erlang in our project, ended up going with Clojure mostly because of available and easily accessible Java libraries.
I still find it amazing that I can:
1) add a single line to my project.clj (which will set up dependencies and download libs),
2) add a single line to my :import section at the top of the source file,
3) there is no point 3. Just call Java libraries.
But the choice really depends on your application.
Leiningen probably has its root from Maven, which IMHO the killer tool for Java. I've done .NET, a bit of Python, and RoR development/toying/experimentation in the past, and you need Bundler+Rake+RubyGem (at least) to emulate the core (important) feature of Maven.
I still find it amazing that I can:
1) add a single line to my project.clj (which will set up dependencies and download libs),
2) add a single line to my :import section at the top of the source file,
3) there is no point 3. Just call Java libraries.
But the choice really depends on your application.