I think the P-51D is the most versatile plane in the game. Every fighter that it comes up against, it has an advantage in a certain aspect.
For instance, against turning planes such as the KI-84, N1K2, or Spit9, the P-51 can outrun & outdive, and outzoom them.
Against faster planes such as the 190D9, 109K4, and La7, it can outturn them, has a better gunsight, and can outdive them.
The P-51s advantage lies in all the features it has. Excellent visibility from the bubble canopy, good fire power and excellent deflection shooting from 6x50cals, excellent dive characteristics, good turning at all speeds due to the large wing and combat flaps, and also good durability. I dont think any other plane has as many attributes as the mustang.
Also, lets not forget it can carry 2x1000lb bombs, along with 6 rockets and 6x50cal guns. And it has a very long range.