Assetto Corsa runs much much better in VR (being an older game), and has a lot more variety in cars and tracks. The main downer of it is in VR the interface is terrible. It's like a halo ring around your face, and you have to navigate with a mouse
You have the big benefit of mods with that one though, custom tracks and cars. I've downloaded a few classic gran turismo tracks for example.
Competitzione is a modern game, so far more demanding, but has a proper interface for VR. The track and car selection is limited to GT3 class though, and there's no mod support. The driving model is excellent though.
You can't go wrong with either really.
Rfactor 2 and Project cars 2 are also good.
My gameplay:
AC (custom car)
ACC
Kart Kraft