The EU is a bust, China is a bust. India, Brazil, Turkey and Mexico are all possibilities, if they can get there shit together, but India is overpopulated, and overpopulation (in relation to available land and resources) severely hampers economic growth; Brazil is a contender, but 75% of its territory is completely unusable; Turkey is perhaps the most likely of these to eventually become an economic powerhouse, provided it stays out of the EU; Mexico would be astonishingly powerful as well, if it wasn't for the fact that 4/5 of its population are stuck in constant pauperism by the combination of a Corporate state with an archaic proto-socialist bureaucracy. Oh, and the whole drug-laced civil war thing.
The EU and China are both fractious, and both have highly fragile economies (as evidenced by their recent economic crises between April of this year and the present). As far as I see it, until Portugal, Italy, Ireland, Greece and Spain pull themselves off the brink of bankruptcy, nothing will make the EU that powerful. France is a neutral influence, both economically and politically, the Eastern European powers are wildcards, and Germany is -- economically and industrially -- the only productive state in the entire Union.