I'm going to throw in that least 10,000 units should be produced. You can't be even second best if you're a niche player like the 3,500 Nakajima Ki-84s or less than 2,000 Hawker Tempests.
A threshold of 10,000 leaves lots of top contenders. A6M (11k built), P-47 (>15k built), Fw190 (>20k built), Spitfire (>20k built, including postwar), Yak-9 (>16k, including postwar), F4U Corsair (12k).