I like the idea of categorising by era, ie. early war, late war and so on. Basically because there's just too many to choose from
Every time I read the development of an aircraft type it's only been rarely and notable when it wasn't innovative. Those guys were cluey man, back in the days when it was all so new. Often just regular joes because all the qualified disciplines involved had barely been invented, you were having auto mechanics and hobbyists doing the job of modern aeronautical engineers in some cases and getting by on merit.
I like the airacobra for its innovation and reform, conservative ideals have little place in warfare or engineering. But it did have a design flaw of being a little too innovative, it didn't fly like other planes and I think this was the biggest reason it lacked popularity for a fighter mount, the Russians certainly did just fine on that score so it was no engineering failure...it was an ergonomic one.
It's unsettling to fly if you're used to regular trainers, the cockpit moves like a seesaw in manoeuvres because of where it is to balance the plane with the engine fitment. They couldn't rely on cannon weight and ammunition with that because the ammo when used would make it unstable (this was the problem with the P-80A). So the cockpit is firmly placed like a see saw in relation to centre of lift so that it's a really unsettling aircraft to BFM with. Very easy to misjudge.
I also believe this was related to its spin reputation, again the Russians had no such problem. But you see they leapt from clapped biplanes to poorly tooled attempts at a fighter slapped together in a tractor factory so basically had no problem with jumping in a P-39 and starting over from scratch on flight training. Americans not so much, they get nice trainers, good training in nicely built machines and get used to classical, stable gun platforms with good moves and a bit of power. That's like throwing a footy jock onto a ballet stage with the P-39, and of course it's the plane's fault.
As for late innovations, I'm with the Ta-152C zerstörer, people think of it in dora terms but they weren't, they were meant to replace the intended role of the Me-210/410 with the Do335 as a more conservative alternative choice. The heavy-fighter(jabo and escort) and zerstörer role. It was to have supplanted Fw-190D production which took lead on general fighter duties (which was its interim type).
It's like the Mustang, which gets vote for midwar innovations. Designed to essentially perform the job traditionally requiring a twin engine, that of bomber escort (in interwar period these were things like the Blenheim, bomber escorts had range, speed and often a light loadout themselves), but it was single seat and deadly as a short range interceptor. At best people might've thought of bomber escorts as the P-38, Germany was traditional with the Me-110, soviets and americans often converted bombers into gunships as escorts. The Mustange blew all of that away, nobody expected it.
The Ta152C does that but with heavy fighter-bomber/attack models rather than long range escorts. It replaces things like Fw-190F, Me-410, Ju-88, packing their specialised heavy equipment in a single engine high performance airframe capable of combating Tempests, I think it would've been a terrific success.