In my experience, all of the "mirrorless" systems work best with the lenses that they were designed for, or were designed for them as a general rule.
For the Ricoh GXR and the A12 Camera Mount, the best lenses to use are the M-Mount RF lenses that this camera unit were designed for.
For the Olympus and Panasonic Micro-FourThirds cameras, the best lenses to use are the lenses designed for Micro-FourThirds from Olympus, Panasonic, Voigtländer, and Sigma. Second best lenses are adapted SLR camera lenses. Third best are the lenses designed for M-mount and LTM. After that come some C-mount lenses and other oddities. I often use adapted SLR lenses (50mm and up) from Leica R and Nikon SLRs on my mFT cameras, and infrequently use Leica M-mount 90 and 135 lenses as well ... but the FT and mFT lenses out-perform nearly all of them.
This holds true for the Sony NEX and A7/A7r system cameras too, as far as I've seen—use lenses designed for the mount for best results, use others because you like their specific qualities on the camera you choose to use them on.
G