Fighters - USN>MN=KM=RM>SN>IJN>RN altho i'd say MN is better than KM and RM.

Dive bombers - SN>IJN>MN>KM>USN>RM>RN

Torpedo bombers - RN>RM>USN>MN>IJN>KM>SN

USN CVs are on top with fighters. They have KM firepower IJN fuel and speed... well thay're the best at just about everything.
Their torpedo bombers have high damage on their torps (but they have to wait longer before becoming AAW resistant.

IJN has fast fighters strong DBs and average TBs

SN has slow fighters (untill T4) a +1 bonus to fightter growth hidden in the "special force" classing and the strongest DBs currently in the game.

KM - Not as sharp as they used to be but they get the job done. They bombers have far less fuel compared to other nations and their TBs are pathetic.

MN - All round good fighters and average DBs and TBs. They get their T2 DBs several levels sooner than most. 

RN - Generally weak fighters (they can still kill you if you're not carefull) fast but weak DBs and the strongest aircraft torpedoes currently in the game.

RM - Somewhat well armored fighters with a bit more DB than usual. Weak DBs (both weak and slow) strong TBs.