Luftwaffe, line-up, using air power to support the blitz, experienced, well trained personnel, they also had experience from the Spanish campaign. Effective, well maybe not all in all cases, but compared to the others still great. Hehe, only the leadership could be a lot better
RAF did a great job defending, but that doesn't make it the best air force, even though they had the superior Spitfire. I admire the Japanese for their ingenuity and their Zero, and effective bombing of Pearl, but it wasn't as advanced as the Luftwaffe.
Yes, it's not useful to consider the Russians and Italians, but no point of dragging WW1 into this. I think even the Finnish air force did better than the Russians