Fly what you want to.
That being said, there are some nice rides out there that don't get used a lot, Yak-9U, Ki-61, ect, that are great rides.
US birds that can manuever hard: try the P-38 series, F6F, F4U (when you get more comfortable with it).
They are all "fun" in their own way, and you will learn more trying different types, at least sometimes. Dont be shy, you might discover a favorite you didn't even think of.