Their clay bar is my favorite.
If I am asked to reccommend an over-the-counter line of detailing products to someone, I always reccommend Mother's. All of their products are excellent.
Mother's is my favorite over-the-counter lineup because their products have consistent quality. Meguiar's has a better selection, but their quality can be hit-and-miss- most products are good, some are outstanding, and some are junk. Eagle 1 doesn't have as good a selection as Mothers, and the Eagle 1 paste wax is almost impossible to find. Other companies, like 3M, make excellent products, but it's almost impossible to find them. If you find one or two on the shelf, you're lucky.
Mother's is great because almost every auto parts store carries the whole Mothers line. You can always find the 3-step wax system, the claybar, and the preserves protectant. With that, you are set to go.