I would go with the CV lenses, their wides are particularly good. I use their lenses on my M2 and have focal lengths from 15mm to 35 in the wides. If you are just getting one then I would recommend the 21mm Color-Skopar. Sure it is only F4, but terrific IQ and not all that expensive...the VF is pretty damn good as well. Incidentally, the Bessa R4A will take the 21mm without an external VF, but I mainly use mine with the 28mm.
I do have a Zuiko 24mm 2.8 and of course it is really good. You often hear that wide RF lenses are better than the reflex versions but this is not always the case. The Rf lenses are certainly much easier to design, but this often just means that they are cheaper and certainly more compact. Voigtlanders offerings, especially in the super wides, are a great example of what can be done for comparatively little money.