I'm contemplating the switch from 35mm digital to MF digital, and I left my home in rural VT to come down to PhotoPlus and play with all the present MF systems (as well as attending some very useful seminars). As I had thought from reading about them, they all have some significant pluses and minuses - I'm thinking probably Hasselblad for my specific uses (landscape photography at a variety of scales), but it's a really close call between all three, and minor variations in uses could make the calculations come out in favor of any of the three (plus Leaf, who has a very nicely priced Leaf/Mamiya system, and a very expensive - much more so than Sinar - system based on the Hy6/Afi body)! I did not compare image quality, because only Hasselblad had the LARGE prints one would need to see the differences. I did compare image quality (especially shadow dynamic range) between Hasselblad and the Sony A900 (the present low-ISO DR champ among 35mm class cameras) - Sony also had large prints taken by capable photograpers at their booth, and the A900 impressed, until compared with a Hasselblad (or, presumably, a Phase, a Leaf or a Sinar)! The Hassy had at least an extra stop of shadow DR - neither one had a shot with meaningful detail in the far reaches of highlights, so I really couldn't tell if it was holding more highlights as well. In addition to the extra stop into the shadows, the Hassy had much cleaner lower midtones - the Sony didn't look muddy unless compared with something better, but it was noticeably muddy in lower midtones and shadows when compared with the Hassy... Note that even on huge prints, the Sony had a lot of resolution - the issue was dynamic range...
Anyway, with medium format having beaten 35mm soundly on image quality (and with all three manufacturers saying that the various backs are essentially equal in image quality at comparable resolution), here are my observations between the MF players.
Body - Sinar (and Leaf Afi) 1, Hasselblad 2, Mamiya 3
I love waist-level finders, and the Sinar offers the only one in the medium-format game (discounting Hasselblad's "lose the meter" option). The Sinar's grip is also very nice indeed. Both the Sinar and the Hasselblad seem much better built than the Phase/Mamiya. The Phase/Mamiya grip is not terribly comfortable with my big hands, while both of the others have longer grips that accommodate my hand.
Controls and displays - Hasselblad 1, Sinar (and Leaf Afi)2, Mamiya 3
Hasselblad has a clear lead here - the menus and grip display are superb, the dot-matrix display in the finder is a great addition that allows for many settings to be made with the camera at eye-level. The Hasselblad is also incredibly configurable to the photographer's preferences - the control scheme is where Hasselblad's decision to close their system paid off - everything is set from one set of controls, and there is no line where the body ends and the back begins. The Hy6/Afi has the best placement of its main control dials, followed closely by the Hasselblad and at a distance by the Mamiya, but is hampered by buttons that are unmarked and too easy to hit by mistake. The Mamiys's setup feels like a consumer-level 35mm DSLR, and critical functions including ISO are set from an unrelated interface on the back, while the other two, with their configurable controls and better displays, are much more elegant.
Lens selection - Hasselblad/Mamiya tie, Sinar and Leaf behind
Both Hasselblad and Mamiya have fairly complete, current production AF lens lines (each has some advantages, but I could certainly live with either one). Mamiya lenses have historically been cheaper, but the D series are closing that gap - conversely, the Hasselblad lenses are better built, but that gap, too is closing with the D series. Mamiya has practically sized zooms for field photography, which Hasselblad lacks - the Hasselblad zoom is huge. Hasselblad has a dedicated teleconverter, which Mamiya lacks. The Hy6/Afi system relies on a lot of older, manual-focus lenses (some out of production) to make up important gaps in focal length, and, even counting older lenses, has no lens shorter than a 40mm... The other disadvantage to the Afi/Hy6 lens lineup is that there are more large/heavy lenses - certainly not all of them, and no system is without pudgy lenses, but there seem to be more in the AFi/Hy6 system.
Lens cost - Mamiya 1, Hasselblad 2, Sinar/Leaf 3
The comparatively inexpensive older-design lenses bring the overall cost of the Mamiya lens lineup down, although the newer ones are comparably priced to Hasselblad glass. The Afi/Hy6 lenses carry a significant premium.
Lens quality (from charts found online) - Sinar/Leaf 1, Hasselblad 2, Mamiya 3
The same older lenses that bring down Mamiya's cost bring down their quality as well. The Hasselblad lenses do pretty well, and the Schneider and Zeiss glass for the Afi/Hy6 is superb.
Features - Hasselblad 1, Sinar/Leaf 2, Mamiya 3
The Hasselblad body is little short of amazingly full-featured - fully programmable, every imaginable adjustment. Some of them are useless, of course, but there are also very useful ones in there - the Zone mode allows readings of the dynamic range in a scene using the spotmeter. The Sinar/Leaf is also fairly feature-laden, while the Mamiya's basic design is showing its age - it feels like one of the early N80-based 35mm DSLRs with adequate but not superb controls and poor integration between camera and digital back.
Accessories - Hasselblad 1 (by a mile), Mamiya 2, Phase 3
Hasselblad has two unique accessories that no other player can match, and they, more than anything else, cause me to be favoring Hasselblad. The first is the integrated GPS. A tiny module that attaches to one side of the body and weighs no more than a couple of ounces adds location to every picture's metadata. The second is the upcoming HTS 1.5 - providing tilt and shift adjustment in a compact 1.5 lb contraption that uses existing lenses. While expensive, it is much cheaper than any conventional view camera solution, and 25% of the weight. Mamiya can't match these exotic accessories, but offers a full line of standard accessories, while Sinar/Leaf lists items as basic as extension tubes and a grid focusing screen as "coming soon".
Batteries - Sinar/Leaf 1, Mamiya 2, Hasselblad 3
The Sinar/Leaf camera is powered by a single battery, which is a standard, easily available, cheap camcorder battery (the newest Sinar solution requires only one at a time, while other backs require two identical batteries). Both Leaf and Phase backs on the Mamiya body take camcorder batteries, but the body requires AA cells in addition (however, lithium-ion AAs will last essentially forever in this application and don't weigh much). Hasselblad's rechargeable grips are a racket - essentially a camcorder battery with a rubber coating and some plastic to form it into a grip, but a nonstandard size available only from Hasselblad, and costing over $200 apiece for a $30 battery. This may not matter to indoor shooters, but the half dozen needed for extended landscape work cost well over $1000. Hasselblad's overpriced charger is also primitive compared to what is available for camcorder batteries - a $200 charger that charges one battery at a time! Camcorder battery chargers cost $50 and charge two batteries at once...
Software - Mamiya (Phase) 1, Hasselblad and Sinar/Leaf 2
Capture One 4.5 is worth the wait, at least on the Mac - great tools, works with 35mm files as well as Phase files (I'm not concerned with tethering), offers lens correction. I'm a little concerned about the revision schedule, because it took them so long to move from 3.7.9 to 4.5. Phocus has a very comprehensive toolset, including lens correction and correction for the HTS tilt-shift adapter! The downside of Phocus is that it works only with Hasselblad files, requiring workarounds to integrate with any other system - if I were to shoot ONLY Hasselblad (no small-format), Phocus offers full library management. Sinar and Leaf take the opposite tack in that their newer systems essentially forego dedicated software, outputting in standard formats that Aperture and Lightroom can read - no dedicated lens correction, but no-hassle integration...
The score (3 points for first, 2 for second or a tie, 1 for third, 2 bonus points to Hasselblad for the HTS) - Hasselblad 22, Sinar 18, Mamiya 16. Not quite fair to Mamiya/Phase, because Capture One should perhaps get some extra weight, but that body costs them compared to the more flexible bodies offered by their competitors. The body issue exists with any Mamiya-based solution, including the new Mamiya/Leaf as well. Upweighting Capture One by 2 or 4 points would allow Mamiya to catch the Afi/Hy6 system, but, for my uses, Hasselblad is well out in front. With the new pricing, Hasselblad is also the price leader, and their factory folks were very helpful at PhotoPlus...