As mentioned, I don't think there's any value in arguing about "BEST" but am enjoying the listing and discussing of the important fighters of the 30s.
Did anyone mention the Gladiator biplane? Remember that it was the foundation of the RAF home defense in September, '39, and remained in service through '44.
It was an effective fighter for not only the Brits, but Finns, Norwegians, Chinese, Iraqi's, and Greeks, not only gaining credit for many kills, but a bunch of aces, downing Me109s, Zeros, as well as the lesser adversaries.
It served in all theaters from Arctic to Equator, Europe to Far East, and kept Malta in Allied hands with Faith, Hope and Charity.
Remarkably, RAF Gladiators engaged in dogfights with Iraqi Gladiators.
Did any other biplane fighter stay in service longer?