I get the one with only three ingredients (Well, if the one with lavender is on sale, I'll get it too!):
Saponified Olive Oil
Water
Sodium Chloride
I buy 'em up at the health food store when they're on sale, and then get an extra 10% off because of their policy. (Over $100 is automatically 10% off and that's easy as I don't shop there weekly).
I have found that if I also use it as a shampoo, my hair looks really nice, fluffy and clean. Lathers nice, too. And one bar lasts a LONG time - a lot longer than the bar of Zest hubby refuses to part with.