You know me, although I use Nikon (less and less actually - I have shot 40 frames with my D2x in 2007 so far vs several thousands with the Mamiya), I don't care much about brands.
I don't know if Nikon is really better, but I know that all the lenses I have bought from them have always been outstanding with no obvious issues.
Bernard, we're in the same camp on that - I have no brand allegiance for anything. Either it performs properly or it doesn't regardless of who makes it.
Now, I'm interested in your Mamiya experience. Are you talking about the ZD, medium format 20 MP model? I saw it and handled it at the Mamiya booth at Photo Plus East in New York last week. Sweet piece of merchandise I must say. When one is at the cusp of buying a 20MP 1DsIII, this is a decision point one needs to consider. Here's how it stacks up in my mind so far:
Price USD 8000 in the US, and due to Canon Corporate price differentiation policies, CAD 9200 in Canada (eventhough the Canadian dollar is now worth 3% more than the US dollar - OK some add-on is justified for the probably higher unit cost structure of a Canadian distribution and service outlet, but 15% seems a stretch).
Like many others in my situation, I have a suite of Canon lenses so need to spend more on that. Most of my work is with the 24~105. Great range for a high percent of my work and I have a superb copy of this lens.
From what I've seen the resolution and image quality are highly satisfactory, but it's prelim. Great noise performance, high speed, self-cleaning sensor, etc. etc.
Price 10000 USD with one lens. To replicate the same range as the 24~105 I would need two additional lenses costing a total of another USD 5500. Using all this means changing lenses as one progresses through the range. It's more and heavier gear to trudge around with.
9 micron (versus 7 for Canon) pixel size. What difference in image quality does this produce? Mamiya of course says it is huge. Perhaps - I don't know.
Bit depth: Canon 14, Mamiya 12. Does this make a practical difference? I don't know. Theories are no good here. One needs to see actual results from valid test images.
Noise: at the booth they admitted noise is an issue from 200 ISO. (I've heard another opinion that it is an issue beyond 100 ISO) The Canon hardly shows any noise up to ISO 800. Does the additional noise reduction requirement eliminate the pixel size advantage? I don't know.
Both have AA filters.
So, where does all that leave me? (1) I'd love to hear about your experience with it, because there is nothing more valuable than expert advice from an extenisve and intensive user. (2) So far it tells me I may as well stick with Canon for a number of reasons that are custom to my circumstances. But this is a real decision point - I think.