I agree with Guy; the task of deciding between bodies should start with leaf vs. focal plane shutter. Both bodies are exceptional tools and each has niches where its advantages make it the better choice.
Landscape
Using a leaf shutter lens (the H body) for landscape you will suffer (extra weight, size, cost - slow max shutter speed) without benefit (high flash-sync-speed doesn't ).
Portraits
Portraits taken without flash or studio portraits are largely the same between the two bodies. Portraits taken on sunny days outdoors with flash favor the leaf-shutter in the H-body
Macro
The Mamiya/Phase and Hasselblad Macro lenses are both absolutely stellar; however, there are two bellows systems for the Mamiya/Phase if you ever want to go past 1:1. I don't think (correction anyone?) that the Hasselblad system has any bellows system (leaf shutter lenses make such systems more difficult).
Usually I would list the dozens of pros/cons of each body, but if you're shooting mostly landscape and already have/like the Mamiya body then I wouldn't look much further. In the future you might upgrade to a more recent version of the AFD body, but most of the improvements don't apply to landscape photography. You might also consider a technical body which is dedicated to landscape photography; they are harder to use (generally speaking) but produce unquestionably the highest image quality available when using the latest large format lenses.
Doug Peterson (e-mail Me)
__________________
Head of Technical Services, Capture Integration
Phase One, Canon, Apple, Profoto, Eizo & More
National: 877.217.9870 | Cell: 740.707.2183
Newsletter: Read Latest or Sign Up
"IF you want to make the flash the primary light source and not just fill."
Doug, outdoor portraits using 1/800th sync rather than 1/125th allows use of wider apertures to separate subject from background, and the fill can be set to taste. One need not use flash as the primary light source as you state. Use of a longer lens for portrait or environmental photos with some movement @ 1/125th with just a touch of fill is something I personally avoid.
Not advocating one system over the other, the original poster can sort that out based on his needs. Just keeping it balanced.
Here's an example shot @ 1/750th shutter with just enough fill for the back lit subject ... shot in direct sun at water's edge.