Well if it has to happen, then I think it will in Asian Sub-continent region. The tensions, the drama, the threats, instability, are just too much. Name it, and every possible reason for starting WW3 is available there. China backing Pakistan, Russia backing India, tensions between India-Pakistan, India-China, America being diplomatic with all of them, all the spices are available.
Asia is quite stable now. Tensions between China and India has mostly subsided, although a lot of bad blood still exists between India and Pakistan. And China is no longer backing Pakistan, and Russia is no longer backing India. So we can be quite sure that even if a war between India and Pakistan breaks out, it will not turn out to be the 3rd World War.
Regarding China backing Pakistan, I think it can never stop. Just recently I have read that China has invested about $56 billion in Pakistan and Pakistan-occupied-Kashmir for developing infrastructure, whereas when Indian PM went to China for investments, he has been handed only $20 billion. Chinese and Indian army are already engaging one on one on the borders. Chinese intrusion in Indian borders have lot of evidence.