I think is still US, cause of advance technology and resources. This will make sense even in war. Number of people does not count in this chemical bomb or anything at all!
True. US has more money invested in military than any other country. I think it's still the most powerful military in the world. Despite this, you can't say that they can win against China. Where will the war happen? Chinese battleships can't beat American ones but if the war starts in Asian territory I think it won't be clear who wins.