I used Mother's clay for the first time yesterday. I have also used Zaino and Meguiar's. I would like to try Clay Magic, but my local AutoZones do not carry it.
Mother's clay is by far the best I have ever used. Zaino is a close second, and performed almost as well, but Mother's clearly did the best. The way it sucked up contaminants was simply remarkable. It glided across the paint effortlessly, and did streak somewhat toward the end, but a wash took care of it. BTW, every clay I have used has streaked.
The reason I prefer Mother's is because of its absorbancy. It's like a sponge which drinks up contaminants. The other clay bars will get them too, but Mother's is so much easier . The Mother's bar would leave a smooth surface in 1-2 passes. Zaino would take 2-3, and Meguiar's 4-5.
The only disadvantage of the Mother's bar is that it is slick and is too easy to drop. The Zaino bar has a different texture, and is almost impossible to drop.