Aw shucks, NorCalZ71. This thread is not going to make your life easier, is it?
I've used Mothers, ClayMagic, and Autopia. For reasons others have mentioned, I never did bother with Zaino clay and haven't tried Griot's clay. Of the three I've tried, I now always reach for the Autopia clay on vehicles I really care about. Its consistency and effectiveness are the best I've tried so far.
My 2nd choice is Mothers. Very malleable clay, and their lube smells marvelous (or at least that's what my nose says). On my 2nd-tier cars, I reach for it first, just to save money, because I think it's a bit less expensive than Autopia's clay. And I know I can always find a "replenishment" locally, instead of having to do an Internet order.
Compared to those two, ClayMagic is just so-so to me. I'd buy it if the others werent available. There's nothing "wrong" with it. But to me, it just feel like Autopia and Mothers do a better job.