Depends on time factor and what's coming in (number and type). If they're still some distance from the field (2k+) then probably a Niki for low alt (50% fuel), or with a little more time and if I want to get above them, a Spit8. If they are nearly on top of the base, the a HurriC or SpitV/Seafire.
Reasoning:
Niki - I probably have time to gain maneuvering speed and a small amount of alt (1-2k). The guns are devasting at close range and there's lots of them for sustained defense. It can hold it's own with a Spit5 or F6F, if careful, and outrun an A6M or FM2 if in trouble. Only the F4U's are a real problem, but not if they're low.
Spit8 - gets off the runway fast, and it's faster and outclimbs just about anything coming in from a CV. It can maneuver and dive reasonably well with just about anything. Good and accurate, if not actually devastating, guns.
HurriC - when there's no time and you might get vulched, or locked in a furball, it gets off the runway quick and turns fast when slow. Great in a furball with the best guns in the game for snapshots and short burst kills. Only drawback is it attracts attention and the ammo load is just a bit limiting. Can out turn anything inbound with the exception of the A6M and FM2, but is comparable.
SpitV/Seafire - Also for close-in furballs, more as a change from the HurriC, but when there are fewer A6Ms, and more F4U's or Seafires inbound. They also get up quick.
I DON'T take drop tanks because the mountings still impose a small drag penalty after they are released and there's no need when you're fighting right over your own base. Pretty much 50% for any fighter will provide plenty of flight/fight time, and keep it light enough to maneuver at it's best.
