The one you are the most proficient in.

For the most part programming languages are the "same" in that they are a means to an end. Yes you can argue about their attributes but they are tools. If one guy can dig a hole with a pick as fast and as good as another guy can dig a hole with a shovel then to each his own.

All that the language vs. language discussion can really turn into is an argument about programming minutia between a bunch of folks coming from a thousand different unique standpoints. I honestly have never seen it lead to anything productive - pick a context or business need and maybe it'll turn into something useful.

Try assembly. It'll kick your ass real bad. Or better yet, try programming in binary!

On a more serious note, what do you mean by kickass? What features are you looking for in the language? What is your target usage/application? What is the environment you are going to be working in?

There is no straight answer to what programming language is most kickass. Different languages are suitable for different purposes and kick asses of other languages given the appropriate application development goal

If "kickass" means the ability to build cool programs in a short period of time, then I would suggest Ruby, specifically its metaprogramming capabilities. Very powerful and fun to write.

It depends - What do you mean by "kickass" ????

A very incomplete list ...

Utmost speed, very close to the metal: C, C++, Assembler

Easiest to learn and write, quickly: Python, Ruby

Will get you a job in most large corporates: Java, C#, COBOL

Will run on all browsers and many servers: ECMAScript, aka JavaScript (TM Oracle Corp)

Might impress the technorati: Haskell, Scala, Erlang, Common Lisp, ML, F#, Scheme

Totally utterly useless and do your brain in: BrainFuck

Assembly Language.

Lisp.. what else...