what Allied aircraft are the best in this game?

[TinyTim]

Yak-9U at low and P-51 at high altitudes.

[Woke Up Dead]

The La-5FN and the La-7 are tough 1v1 opponents for any German plane, though I find the 5FN loses a lot above 2000m.

The 190 is not really a good 1v1 plane against any allied fighter, but it's probably the plane that benefits from a wing-man the most in this game. For example, 1v1 I'll take the La-7 anytime, but in a 2v2 scenario I'll go for the 190, even if it's an A-9, and definitely if it's an 190-D.

Agree with Tiny Tim: Yak 9U is great against German planes up to about 5000m, the P51 is great above that. The P63 can also do very well against late-war German fighters.