Complementary, in my limited experience.
I've only flown gliders, motorgliders and variety of single engine types, but I'm sure the variety is beneficial. Earlier this afternoon I was flying a Jodel Mousquetaire, which was "slope soaring" quite nicely in the winds we had here. It seems natural after doing it in gliders.
The more types I fly, the easier it is to convert. You need to understand your checks, rather than just doing them routinely from habit. You also sometimes fly a type that clearly displays a trait that is barely visible in others. In a Zlin that I flew, for example, the gyroscopic effect of the propeller caused a clear pitching effect. In a medium turn to the right, a touch of forward stick was needed to maintain level flight. The same is true in any other type (although the Zlin's engine turned the "wrong" way), but I'd never noticed it before.
If I flew helicopters, I'd probably understand why they always seem to come and land next to me if I'm in something small and light!
