I personally think that the Italian Blu-ray of For a Few Dollars More looks the best because of the better looking colours and has no over the top sharpening and edge enhancement like the German one has.
The way I see it to make the best version, you would add the English friendly opening and end credits from the regular MGM Blu-ray, the scene from the German Blu-ray that is not on any other release and the rest from the Italian Blu-ray with the original mono.