Weren't P39s owned by real fighters and, as a result, were relegated to mainly ground attack roles? And explain to me how a buffalo wouldn't be as big a flying sacrificial target as an F4F or the early P40? There are already plenty of pig rides (of which the P39 would be one). And bombers?? Flying bombers is like watching paint dry. We have pleny of bombers to go around. Any added bombers would be just making more interesting targets for the interceptors. From what I understand, Some of the late Jap planes were real monsters. So, as far as this vote is concerned I'd have to say G55, and one of the late jap planes, KI-44 or 43. 100 would be neat too.
That said, I'd still like to see the little Poli I-16 as an emotional favorite.