Great questions, and fascinating to read the responses.
For me, number one (now) has to be the ability to manipulate the focal plane, and number two, image quality.
I actually dropped out of the MF game a while back and currently shoot with a Panasonic S1R. But that camera is mounted to a CAPcam, and I shoot with the Linos 5.6/105 Float. To all intents and purposes, it is a medium format system, just with a smaller sensor. Yeah - I know that won't make sense to many, but it does to me
, and - resolution aside - I'm as happy with the image quality coming off the S1R's sensor as I was with my IQ3 100.
I'm hoping that the new rumoured camera from Fuji will be the modular GFX 100 based system that was shown in Dubai in February 2019, since I would love to mount that sensor on the CAPcam.
Top 5 favourite images (in no particular order) were made with...
CAPcam, S1R, Linos 5.6/105 Float (a watch)
Hartblei HCam-B1, IQ180, Canon 17mm TS-E (a cityscape with fireworks display)
Walker Titan XL Wide 5x7, Velvia 50, Schneider 5.6/210 XL (a cat)
Phase One 645 DF, Ilford PanF Plus, Mamiya 1.9/80 (a portrait)
...
The 5th I'm going to leave unfilled. I can't imagine taking a photo in the future that would knock any of those four out of the top five, so will save a slot for what's to come.
Kind regards,
Gerald.
/edit
Apologies. I've just realised I answered the question "what matters most to you for ultimate digital image quality" by answering "image quality". Hehehe.
Ok so to break that down a little, right now it's very different to what it used to be, because of what I shoot these days. And beyond the ability to manipulate the focal plane, the next most important one has nothing to do with the camera system -
1. The ability to manipulate the light
2. The lens (I could never go back to shooting 1:2 to 2:1 macro with anything other than the Linos)
3. Sensor dynamic range
4. The ability to manipulate the subject (by which I mean the ability to remotely move the subject around in 3D space, because I don't move my camera)
5. Tethered live view
6. Capture One
7. Sensor resolution