Who will win a war between India and China?

Probably China, but I wouldn't say it's a guarantee, and it's a question of how damaging the war gets for both sides. The two theaters of such a war would likely be the Kashmir region and the sea, since the Himalayas block most the border, though you may also see some of them passing through the south east asian countries that separate them. Most of China's population and infrastructure are pretty far from India, which would insulate them somewhat, but also make their supply lines more costly, and if India doesn't back down quickly, say the become galvanized, then the cost of the war could grow very high for both of them. It would likely have an inconclusive end, which is probably why such a war hasn't happened, neither side believe a meaningful victory is within grasp.