Lv. 1 Singaporean, Israeli, USAF with recent combat experience, UK with recent combat experience.
Lv. 2 Taiwan, SK, France, India, Japan, USAF no actual combat experience (not counting Red Flag, etc. as combat experience)
Lv. 3 Russian top tiers, China top tiers.
Lv. 4 Dump all the air forces with good overall pilots here.
I'm not being biased to Singapore. It's a fact. We have so few planes to fly, relatively, that the RSAF picks the best of the best only.
There was one op Red Flag where the poor USAF guys got hit pretty hard by the SG folks.
Red Flag might count as actual combat experience, but most of the time you don't have planes exploding around you. Factor that into the equation if you want. Russia and China have so many the i don't have to say we can't just take the whole air force and dump it into category 3...