I haven't used the HD100, but I do own a Z1, and it should be hard to go wrong with either. The Z1 shoots 1080-line HD footage, but only interlaced, the HD100 shoots 720 line, but progressive-scan. The Z1 has a fairly decent fixed lens (but which does get some chromatic abberation at times), the HD100 lets you change lenses, but new lenses will probably be expensive. The Z1 looks like a big consumer camera, which may be useful if you're trying to shoot without getting too much attention, the HD100 should be easier to use hand-held with the shoulder mount.
About the only bad thing I've heard about the HD100 so far are people claiming that the color balance changes across the frame. I don't know whether that was a fault of the prototypes or still exists in the production models.
