For "A Fistful of Dollars" I would recommend the Italian BD over the German. They are both from the same source, but the German is slightly darker, so you can lose a little detail in the dark scenes (comparison). I'm assuming the Italian is more accurate, as the restoration happened there.

It's worth noting that in "For A Few Dollars More," the primary source of the German BD is the MGM transfer, and they look the same. This transfer is the best of the MGM transfers, but both versions share its excessive EE (comparison). The German version is still the best, of course, as it's uncut.