I recently tested various backs from Leaf, Sinar and Hasselblad against my trusted Leaf Aptus 65.
I really couldn't see much difference between them, they are all so bloody good that I would be happy to own any of them! If you are new to camera backs, you will have great difficulty in deciding and your decision could be made on points such as practicality, a good demo, whether you like and believe what the rep says, whether you like the software and so on, rather than the ultimate quality.
The vital is to know what to look for and regrettably that is not that obvious in marketing from the MFDB makers or from reviews, e.g. as published here on LuLa. In my personal experience a demo gives very little apart from the feeling of handling the back, same as a test drive of a BMW 5 or Mercedes gives little without knowing or understanding the differences between the characters, performance and handling of these cars. The essential in my view is to prior any testing knowing what key characters differ between different backs, and which helps narrow down and see what really differs between them, and in particular so during test driving raw files, perhaps with images captured with our own set of conditions or of captures similar to our own shooting and critical conditions.
I have had the Aptus 65 which is an excellent back. The Aptus-II 10 apart from more pixels appear to me to add slight more DR and improved color performance. On other hand I find the Aptus-II 12 files to apart from pixels be a larger step from the Aptus-II 10 than that was from Aptus 65 in improvements in color profiles, DR, and the fine gradations of colors. Yair was kind to pin point me towards this, but I experienced the improvements with the Aptus-II 12 as larger than he described. It is important though to draw
our own conclusions per our own test drives. Small size images do as much justice to a back as photos in a Motor Trend do of the handling of a Porsche or BMW on a twisty road...
And no, pixels apart, no DSLR measure up in optimum image quality at low ISO.
Regards
Anders