To me there is a running theme on these threads: there are many differences between an amateur and professional photographer, and it has nothing to do with skills or abilities. Amateurs can use what ever equipment they want, what ever feels good, what ever makes them happy. Professionals need the tool that gets the job done, every time, and is bulletproof reliable. How a lens draws or which is sharper or which feels nicer is an irrelevant if you are worried about your gear crapping out or worst of all if it actually does on a shoot (been there, done that with nearly every manufacturer, have the grey hairs to prove it).
If you look on the threads, with little exception, you will see pros recommending the camera that is good enough for their work and clients, is reliable, has a good warranty and a strong dealer network. I'm not really shooting professionally an longer, but I have enough shoots that I have not been able to make time to send my partially working Leica DMR/R8 back Leica to get fixed (both bodies need repair) because I have no idea how long they will keep it and for that reason it is not a professional quality camera -- regardless of the image quality. With Canon or Nikon, they would send me a replacement, I would send in my camera to get fixed, get it back a week later and send the loaner back. That is what makes Canon and Nikon professional level tools, regardless of the image quality.
So back to the question at hand. If you are an amateur, get what ever makes you happy. My vote goes to the Contax because it feels nice and is a joy to use and the lenses have that great Zeiss quality (it's not sharpness, it's something else). If you are a professional photographer that involves working with models or clients on deadline (pretty much anything besides fine art), or aspire to become one, manufacturer or dealer support is king and that means Mamiya AFD or Hasselblad H2 or H3D. With Contax, bodies may be cheap enough to keep a spare or two, but if your back craps out will you be able to get another digital back with a Contax mount on very short notice? Honestly, I have no idea. But you should.