I disagree with the title itself. The 21 century contest is between Sino-Soviet alliance vs the US lead western alliance. India need to decide which side it want to join. And India can be a difference maker. However, to marginalize US and the western countries by making the 21st century a contest between China and India is just not realistic. US still has a lot of weight in the international diplomacy. As a matter in fact, the only superpower in the world today is still the United States. Not China nor India.
India will be with USA, it is forgone conclusion. If you look at the Indian elite and next generation of it, most of them are US educated or connected financially to USA or UK.
India is mature enough to conduct trade, and be China's tonto in G-20/Economic summits where there is an overlap of interests, Militarily and Strategically China and Russia are too damn close and clash with Indian sphere of influence.