Brewster B-239, at least for now. Excellent aircraft.
Though I have to point out that it was not Brewster Buffalo, which was a ridiculous fighter plane. Its type name was B-339, and it - along with F2A-2 - sucked bad. B-239 was much closer to prototype F2A-1 - so close that actually the prototype model (XF2A-1) was included in the planes that were used by Finnish pilots...
In case you didn't know, Finnish Brewster pilots scored a kill-to-death ratio of 496 russian planes shot down against 19 lost Brewsters. Ie. approximately 26:1 K/D ratio.
It had excellent maneuverability, good cockpit visibility, it was easy to fly, had relatively good armament (earlier, 3x .50 + .303 machine guns, later 4x .50 machine guns), and it was extremely reliable plane - the engines could be used much longer than planned. It could also take quite abeating until disintegrating, although pilot protection wasn't the best of words. It was also quite fast and durable in descent, too, even if it wasn't the fastest fighter in level flight.
Of course, the success of B-239 has also *something* to do with pilots and tactics, but it does tell something of the plane as well. The highest scoring Finnish ace, Ilmari Juutilainen, who flew 437 sorties, scoring 94½ official kills - without EVER getting hit by enemy fire.
Although once his Bf-109 was damaged by friendly AAA, so he had to land.

That's my absolute favourite plane at least for now.
Newer planes can't compete, although some come close.

Another very nice plane I'd like to have when I get older and filthy rich is PIK-20D...