India and China are the world's two most populous countries.
A French Dassault Rafale performs a touch-and-go landing. By 2020, India will be operating a number of Rafales. (US Navy photo)
In the 1962 war, air power didn't play much of a role. Today, though, both sides have modern capable air forces, and they could go head-to-head.
According to GlobalSecurity.org, by 2020, the Indian air force will operate a mix of Su-30MKI Flankers, Dassault Rafales, Mirage 2000s, MiG-29 Fulcrums, modernized MiG-21s, and the indigenous Tejas fighter. Older planes in service would include the Jaguar ground attack plane and possibly MiG-27s. The backbone of this force would be as many as 280 of the Flankers.
GlobalSecurity.org notes that the People's Liberation Army Air Force, like the Indian Air Force, relies heavily on Flankers — though these are primarily the J-11, China's copy of the Su-27. By 2020, China could have as many as 312 of the baseline J-11s, plus about 24 Su-35S Flankers, roughly 65 Su-30MKK Flankers, and 75 J-11B Flankers. China also would be able to add a large number of J-10 Firebird multi-role fighters, older J-7 Fishbed and J-8 Finback fighters, and JH-7 Flounder fighter-bombers.
PLAAF Su-30. (Photo from Wikimedia Commons)
China technically has a larger force. However, with the tensions in the South China Sea, as well as a maritime territorial dispute with Japan over the Senkaku Islands, the Chinese cannot focus all of their force on India, at the risk of facing a conflict on three fronts.
FlightGlobal.com notes that the People's Liberation Army Navy Air Force has roughly 190 fighters and fighter-bombers on hand, but over 100 of them are older J-7, J-8, and Q-5 aircraft that would be overmatched by Japan.
India faces a somewhat similar division problem due to Pakistan's relatively close military relationship with China, but that is arguably more of an extension of a single front. Most of Pakistan's combat aircraft are also older designs like the Mirage III, Mirage 5, and J-7.
A Hellenic Air Force Mirage 2000EG. India also operates the Mirage 2000. (Photo from Wikimedia Commons)
This becomes the biggest factor in any Sino-Indian air war. China could theoretically crush the Indian Air Force by focusing all its fighting power on the task.
The problem China faces is that such a focus would prove a Phyrric victory, as its claims in the East China Sea and South China Sea could become highly vulnerable. But if China sends in only part of its force, it risks seeing the People's Liberation Army Air Force be defeated in detail.
India, on the other hand, faces no such problems. As such, it has a good chance to win an air war with China, simply because the Indians don't face a potential second front.