I own a H1, but have only played a couple of times with the Mamiya.
I felt that:
- the viewfinder of the H1 was larger and brighter,
- the Fuji lenses are really top notch in terms of sharpness, but then again the Mamiya lenses are said to be no slouch either,
- the feel of the H1 is nice and it does have some neat features like built-in zone system spot metering, combined MLU and timer,...
- the AF is fast and accurate.
On the downside:
- the battery life of the H1 is pretty short,
- my body (with an old firmware) is pretty buggy, sometimes lenses or the viewfinder are not recognized,... the H2 is said to be better,
- the H1 is heavy, and so are the lenses.
All in all, the H1 is IMHO not the best camera for landscape work, which is probably why I hardly use mine anymore... until I get a digital back at some point of time.