I don't think English language is the most powerful language. In fact i think it is the most widely used and most known language to all. It doesn't imply English is powerful. At times when there was no English, may be there was some other language that had the same prospect English has nowadays. It is obvious that with the steep rise of China, Mandarin would me the most widely used language in future.
Maybe powerful just isn't the right word to use. Of course, a language itself can't have power. A language is just a set of words and grammar used as a tool to communicate. A language can certainly have more or less reach. I definitely think that English has the most reach in the world. I doubt that Mandarin will ever be more popular than English. Off the top of my head, it seems like most developed countries speak indo-European languages. English is also an Indo-European language. This makes it easier for most of Europe and all Spanish speaking countries to learn. Chinese has a too complicated writing system to be the world language unless it is forced on everybody.