I've used Mothers,
Meguiars body-shop line and the retail line, and 3M clay. The
Meguiar's body shop stuff comes in various levels of agressiveness (I believe I used the white colored one). The yellow
Meguiar's was my least favorite because it sometimes streaked. Whenever that happened, all I did was just spray on some QD and buff it off, no biggie.
I recently tried the 3M clay...works great! No streaks it did what it was supposed to. I paid a little over $20 for a small container with 2 bars in it. In terms of agressiveness, I would rate it equal to the Meguiar's white clay that I've used. After claying a car, the paint is so darn smooth!!