"Guru Reports" gave P21S the highest final grade of the "natural" waxes, as I recall, and Zaino got the best final grade of all (whether carnuba based, or, like Zaino,
synthetic). Klasse did well, with a final grade somewhat below Zaino, I think. Their overall conclusion was that the synthetics, such as Zaino and Klasse, were superior overall, especially with regard to durability. There are so many variables at play with different finishes, colors, climates, car care habits of owners, etc., it seems to me. As indicated in the test results cited in the preceding post, the differences among the best products are not that dramatic--I guess you settle on the one you like best after trying several. I'm currently using P21S and like it pretty well--it does not have the same retina-burning shine as Zaino (which I've also used), but there is more depth on my black paint with the P21S, which is a point of discrimination for my own tastes. That's another thing, the factors--clarity, depth, shine, etc., probably weight differently in perceived quality from one individual to the next. The only thing I know for certain at this point is that it's great to have a lot of choices compared to what was available when I was a kid.
TT