Well, I'm still in my free trial period so I've only done 100 or so sorties, but so far:
I started with the Spitfire IX just to get a feel for the flight model. Got most of my kills in that.
Got a few kills in a P-51D just to get a feel for high-speed maneuvers. Got 2nd most kills in that.
Took 1 ride in the B26 just to try some low-level attacks. Took out a vehicle base but got budkus kills from it. Had a lot of fun, though.
Now I've been flying in a new ride that combines the best parts of all three of the above airplanes. Don't want to disclose it, though, because then everybody will be flying it and it'll lose its novelty...