[Mikera]

Clojure on the back end and ClojureScript on the front end.

Some reasons:

1. It's a proper full-stack solution. You can share code between client and server if you need to.

2. There is some amazing front end technology (Om, figwheel etc.) that can change the way you think about front end development.

3. It is hard to match Clojure for productivity / interactive development. You can code almost everything at the REPL without restarting (no restarts or edit/compile cycle time needed)

4. You can use all the Java libraries very easily (although idiomatic Clojure wrappers exist for almost everything you are likely to need)

5. The usual Clojure reasons: functional programming, concurrency, immutability, Lisp macro etc.