I'll start out saying that I mimick most of what Woody says and then expand on my specific points.
I wanted a very easy to use and intuitive system that I could just pick up and run with. For studio work, product photography, and outside strobe work of people or race cars/driver. The first system also needed to solve a DOF issue for me on product work for magazines, which meant that I wanted to mount the back on a technical camera. My other need was fast flash sync for the outside strobe work. MF became really needed when I got tired of shots being cropped and turned into a two page center in a magazine or a cover shot getting blown up to an 8ft. banner.
However, I also had a need for higher ISO, light weight, and fast shutter speeds without strobes in available light. I also needed a backup system for some work that I could not afford to have a system go down during.
This led me to needing both a leaf shutter and focal shutter system that would be different animals for different uses.
LCD screens, ergonomics, just plain simple ease of use, software/workflow, and dealer support also played big factors.
I ended up dealing with two dealers that were both great. Sean from Camera West for an H3DII39, and Lance from Capture Integration for a Phase system with a P30+. From what I've seen on this board, I would also have no hesitation with Steve at PPR. I'll also through another plug in here for David at Dale Photo in FL, who spent hours and hours on the phone with me when I was changing my lighting to add a battery powered location set.
I selected the H3DII39 for the resolution of 39MP to do product and large size print work. I really like the ergonomics of this body and how everything is hot buttoned on the body or very easy to find on the body LCD. The screen on the back is probably the best that I've seen in MFDB. This one meets my need also for the leaf shutter system where I can use strobes with a fast sync speed in daylight. It also provides me the option of using the 90 degree finder or a waist level finder. Phocus seems to be excellent so far, although I'm still learning all the tricks. The other bonus from workflow is that Aperture/OS X natively support the files. Photomechanic is also updating their program to support the Hassy files. I realize that it is currently restricted to ISO 400 but should get the update to 800 shortly. Since I needed a leaf system, I also saw David's Sinar in Puerto Rico but felt that workflow/software was not to my liking, I had a problem with it not just being intuitive in how to run, we could not really use the LCD screen for anything on the back, and I hit the buttons on the left side of the camera changing settings by accident. I do see great files from David's work, but it was just not for me.
Next I needed a light weight, fast focal plane shutter for high shutter speeds, available light work, higher ISO, lower cost, with good ergonomics and workflow. I was used to Capture One so this was easy. I used all of the Phase backs and the AFDII in Puerto Rico courtesy of Lance. Once again these were just pick the camera up and shoot ease of use. I did have some complaints on the body and lenses from ergonomics or the ease of adjusting focus on the lens manually for a tweak without having to change switches on the body, body the majority is being addressed in the new body and lenses. I have found the P30+ to excell at what I want it for and that it is faster in basically all aspects than the Hassy system.
Build quality of the camera systems, the Hassy just feels more rugged and precise. To lug around all day and use in available light, the Mamiya wins.
I'm really looking forward to putting both of these to work.
Best,
Ray