In the latest patch about cv, i believe fara made the km nation T5 fighters the best in the game with speed, durability, and front gun power it could be a matter of single digit points though.

Also i think some nations strugle with others like
UK- IJN
SN - KM
US- RM  
IJN-MN
MN- UK
KM-US
RM-UK
left side is more likey to win 

If you have the same base sailors, with the same amount off vets, and seaman with same amount vets.
USA is the best fighter, very close come KM.
But KM can shoot backward, so at least 1 off those for fighers.

Bombers personal i say also USA, but im sure other player prefer other nation.
Torpedo Bombers, UK and IJN