LoL.
Scoring as fighter or attack will determine which rank your points/score are going to influence. Theres separate ranks for Fighter, Attack, Bomber and Vehicle/Boat.
Also, in Fighter mode, only air to air kills will count, same goes for bullet hits (ie hit%). Shooting a vehicle/ground object in fighter mode will give you kill message, but you wont get it scored.
In attack mode, Kills against planes *and* vehicles are counted, also destroyed ground objects.
From AH Help File.