Go to 34th street. More products. More selection. Lex is nice for seeing an organized array of soaps but doesn't seem to have the variety that 34th St does.
Also, at 34th you're more likely to meet the proprietor, Leon, and he's a great guy and good resource. Maybe he'll offer you the 10% B&B discount he did to me!
Oh, and don't bring a big backpack or bulky bags... You won't fit in the aisle at the 34th store.
Just noticed, on the "Sponge Episode" of Seinfeld, Elaine went to Pasteur in search of the sponges.