People have also forgotten to mention picking the best choice aircraft for a particular mission or situation as a reason for taking up a specific aircraft.
If I need to get high over a base to intercept a porker or some light bomber quickly, I take the SpitXVI for it's climb rate and high alt speed. There are others like K-4 or LA-7, but of those I like the Spit more, so I take it.
It's gun package is not the optimum bomber killer (like the G-14 with gondys), but will suffice very well in a pinch. But it's great for chasing down a porking Pony, Dora, Jug or Hog. Lack of range/endurance means you don't usually see it on long escort or JABO missions, so it's not the very best all-purpose fighter aircraft either.