I'm with Guppy/CorkyJr oftentimes it just depends on what I've been reading lately, but the P-39 has become a favorite. The fact that so many kids climbed into that plane in the jungles of New Guinea and some of them lived to tell the tale is amazing to me. They didn't get many of the headlines till they re-equipped in P-38's and other more advanced fighters but they were all we had in 1942.
The 5th Air Force has really captured my imagination, groups like the 35th, 8th, 3rd, 345th, 22nd, 49th, etc.