While I know nothing of the Mamiya 7 and 43mm lens combination in particular, I know that Mamiya's rangefinder lenses are really very good.
But please please please refrain from using the word 'best'. It is such a subjective term and gets misunderstood easily.
And, I second the opinion above about Ken Rockwell. I find most of his reviews pretty uneducated and even offensive at times, and the only sensible reason must be that he's playing a practical joke on us.
Please form your own opinion before you go spend money on something that Rockwell writes up.