What Morph said.
Since you are used to a fast plane, and probably more familiar with energy type fighting, consider the F4U family. Once you get comfortable with one of them (prob the F4U-1A to start), there are only differences in degree from one to the next (ie one is a bit faster, one carries more fuel and so is heavier, etc) . The crossover means that you have a familiar corsair in EW, MW, and LW arenas; you have planes for almost every ENY situation; you have carrier availability and fighter bomber versions; and you have several perk planes including the consensus choice for best prop plane in the game.
And learning the corsair will give you real ACM experience. The F4Us are wonderful at the rollilng scissor, and once flaps go down they dont turn too badly at all. But, they are heavy and take a while to get up to speed -- so if you slow her down, plan on killing everything there or dying!
The P38 is also mostly energy fighter, and it has great guns right there in the nose. It excells in the vertical -- but while many masters love it, it takes a while to learn well and is easy to fly badly. If you DO fly it badly, it is a very, very big target.