Canon-wise, my experience is limited to G5, 300D, 10D, 5Dc.
So, predictably, my worst would be the G5 and best the 5Dc.
From what I have read to be the general consensus, the worst appears to be the 7D and the best is either one of the 5D's or the 1D4.
From the screen-shots I've seen, however, I think the 1DX could blow all of them out of the water comprehensively.
Looking forward to seeing more samples from it and hearing people's opinions.