One of the most popular of the haworthias has to be the "Fairy Washboard", or H. limifolia var. limifolia, with its dark green color and washboard-like ridges on the leaves. I assume it's popular since I see it all the time in the big box stores. This variety hardly looks like the same species, characterized by smooth, lime green leaves. Just as easy to grow, I would think it would be easier to obtain...but what do I know?