I guess it depends on the definition of "powerful".
Scala unlike Haskell, has first class modules ( aka OO ) and unlike Coq (And Agda, I presume) is turing-complete.
( Not that those things really matter to make an awesome language :) )
But for mature statically typed langs running JVM, Scala is the most powerful ...
Not sure about Coq, but Agda is Turing Complete (you just need to turn off termination checks) and Epigram also supports general recursion as well as structural recursion with total functions.