Right now I am at 4 fighters / 2 Dive Bombers at CV3

I have 2 fighter pilots in the air (3 planes) and 2 loading pretty much all the time.  Then usually a 2 plane DB pilot out, as much for extra scouting as damage.   But there can be gaps in fighter cover.  With seven slots I will add my 5th fighter pilot to cover just a bit more.

You can only have 8 pilots on the support slots of a cv at once.

6 is usually the average amount of pilots for all players

I personly like 8 

i have 6 fighters / 2 DBs in my europa but they still not enough. not enough fighters and not enough bombers. i have to load up 3 fighters on one pilot, it's too slow! and i have often to load 5/5 bombers that's really really slow!

the best number of pilots you can have it's the maximum you can fit

Using eight gives you more flexiblity by being able to distribute loads. Like for a 10 plane launch, instead of 3 pilots loading 3-3-4. you can do it like 2-2-2-2-2 -- a much faster load rate.

When I know the other side has a BW, i would usually launch planes by twos cause they load much faster. Sometimes I even launch single planes, especially at the start of the battle just so my team's rushing BBs could get sight ASAP and/or find the BW CV and camp it by my next launch. And these are just fighters mind you.. If you mix some bombers or a scout into your repertoire, that six slots suddenly seems limiting.