I prefer the naval fighters for the Americans. I fly in RB mostly and I prefer the flight characteristics of the F6F particularly, its much more forgiving to fly than say a P-400. The P-400 is brutal on takeoff and poor at altitude. The F6F isn't too great in a dive (rather its satisfactory), retains its energy just well enough but turns very nicely and performs well at slow speeds. I found the P-40 and P-400 are terrible at low speed, so if you find yourself in a turning fight you will have a hard time shaking someone. Ideally its BnZ with the P-40 and P-400 but inevitably you end up in a furball at some point, partly because I keep finding I'm going up against enemy fighters with a better climb rate, so when battle joins they are about 1000m above me.
Re: Brits. Go for the D.520 (that is a NICE plane) if you can afford it, otherwise stick to levelling up Spitfires with a Typhoon on the side
I found the Wellington disappointing, although it can usually take a good beating and other bombers are lacking. The Beaufort makes a nice torpedo bomber, if you like that kind of stuff.