I fly so many planes that I can't say I have a favorite.
I usually pick a plane based on the situation: Quantity of enemy, time to climb, defensive/offensive, Attack/Fight, Escort...
For heavy Furballing at low alts close to home (No time to climb)I love the Spit V. If I have a half sector to climb and put some E in my pocket, then I'm loving the N1K2.
For B&Z I would have to say the D9 or P51-D, but I find the N1K2 to be rather effective here too.
Jabo: P47D-30 or P38 for the total load. I like the P38 for hitting buildings in non fighter areas, but I like the P47 for Hangars in fighter areas. P47 has much better Legs (SPEED) and a huge ammo load. 8x .50cal guns put a hurting on any plane.

It's an awesome thing to Vulch at 400 mph in a Jug!!!

Viper