I go with AKAKs comment, best plane is one you can have most fun in.. Which doesn't mean the plane you can get most kills in.
If I was to pick one non-perked aircraft as the best.. And by best assuming best overall I'd take the Pony D. Simply for it's fuel range, and two most often overlooked advantages compared to almost anything else. Over the nose gun view and all around visibility.
For pure fighter and easy mode. The Spit16 as it's basically a Tempest with better E retention and two less Hispanos.
Best Perk ride and best plane in the game F4U-4 fantastic performance,gun platform and with it's uber flaps can almost float about like a zeke when it needs to which just makes it ridiculously easy to get kills in.
Always a good thread topic, but I think it's been covered numerous times in the Aircraft forum.
<S>...-Gixer