no china has much more men
China
india only win
China would win the war again because it has more soldiers, more money to pay for the weapons, and more land to train on. It also has a better technology than India, and also more allies.
Most likely India they have a stronger army
No one would win especially if either of them uses nuclear weapons. The whole world will lose.
Without either side using their nuclear weapons, and with the Indian Army resisting a Chinese Army invasion, I think India would have a good chance of winning. If it were the other way around China would win, but India would have little reason to invade China.
China
It is likely that US might win the war. Russia could defeat both India and China together, but they would get a lot of their soldiers lost in the battle. US has much better weapons and better, trained soldiers than Russia, making it more powerful.
There is two China's the PRC and the Republic of China that's why it was a civil war so I guess its because no matter who won China would still win.
In such a war, it is safe to assume that China would be attacking and India defending. The Chinese would certainly have the quantitative advantage, but they would have to negotiate some of the world's most mountainous terrain which would favor the Indians' defense. I think India could handle such an invasion on its own, but if not India would certainly be offered help from non-Communist countries around the world. It is doubtful that China would play its nuclear card because India has nuclear weapons too. The Chinese know all this, which is probably why this war has not happened yet.
China would win. China has more soldiers, bigger armies, better technology, and strong/growing allies.