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Having worked for Lockheed, Boeing, BAE, Northrop (as a contractor) and Sikorsky (again as a contractor) I have loyalties with Lockheed. Aside from the record breaking designs, I got to work on airplanes I actually built in the early 1980s 20 years later when I was in the Naval Reserves.
Maybe I'm biased, but mine is Fokker. Best manufacturer of WWI. They were one of the biggest airliner manufacturers in the '20ies. and had some real advanced designs at the start of the war. I'm thinking of the D.22 and D.23, the T.9 and of course my favourite, G.1, all of which could have been winners if the Germans hadn't invaded the NL so early.