The USAF is undisputedly THE most powerful airforce on Earth. The US Navy/Marine Corps IMHO possesses the 2nd most powerful air combat capability, daylight comes third and then the regional air forces start to come into effect. China whilst possessing a massive air force has deficiencies in air to air refuelling, AWACS/JSTARS type capability, SEAD and EW capability etc etc, the list goes on and on. Most of it's aircraft are extremely old and comparitively low tech. In addition it is reported that the sheer size of their forces restrict their training and logistical capacity with follow-on effects on it's overall capability. I'm not saying it doesn't possess massive capability, but it's ability to generate warfighting capability is hamstrung by it's size. China has acknowledged this and is massively down sizing it's forces whilst making important strides in improving the quality of it's forces. The days of massive swarming attacks are over... My list would be:
1. USAF. (Second to none platforms, sensors, networked capability, training and logistical capacity).
2. US Navy/Marine Corps. (As above).
3. Russia (because of it's size and relatively capable platforms, not because of it's training, logistics or C4I capacity).
4. China (Same as Russia).
5. Israel. (Second to none experience and quality of training, platforms, sensors, C4I capability.)
6. UK. (Fantastic platforms, training, sensors, C4I and logistical capacity. Outstanding operational experience in all forms of warfare).
7. France. (Again fantastic platforms, training, sensors, C4I and logistical capacity. Outstanding operational experience in all forms of warfare).
8. India. (Excellent platforms, sheer size and rapidly improving sensors C4I.)
9. Australia. (Excellent platforms, excellent training, good C4I, good networked capability, good recent operational experience, outstanding performance against other air forces in exercises, rapidly improving capabilties with new AWACS, air-air refuellers, Lead in Fighter Aircraft, and high quality upgraded fighter aircraft with new precision attack weapons and standoff attack missiles).
10. Sweden. (Very high quality platforms, good sensors, <AWACS etc>, training, logistics, highly advanced C4I capability. Lack of operational experience is only negative).
That is my opinion anyway. No doubt a lot of people will disagree with me, but remember one thing. Numbers of aircraft aren't the be all and end all of Air warfare. Look at the Falklands. The UK only had approx 20 air defence aircraft available to them and they were able to defeat the numerical and theoretically qualitatively superior Argentine Air Force. This has been recognised as being almost soley due to the superior training of British pilots. Modern warfighting is multifaceted and real capability is generated by a large combination of factors. Paper statistics do not convey the full picture. Cheers.