Answer 1

for me I will say no language is powerful than the other it just depend on what you are using it for and saying a language is powerful than the other is just like saying Spanish is better than English by the way they are all just languages use in speaking to a computer

Answer 2

The most powerful is LISP of course. Even though is is not the mainstream today, it provides ultimate flexibility to extend the language itself. It is really worth checking out for any developer who wants to master the art of programming.
http://wiki.c2.com/?LispIsTooPowerful

Answer 3

Well, LISP is also complete nuts... Just like perl.

To answer the question: It is really dependent on the task you want to solve.

C++ would be for fast desktop applications and games.

Php would be for general purpose, "everyone understands it" - webstuff.

Ruby on Rails would be for the sofisticated web engineer.

Java for platform independence

Python for flexibility and readability

Perl would be for masochists...

So there is no most powerful one, all of them have their areas where they shine.