Probably half of my customers go with some sort of alternating balusters in their stairway design. And of the customers that ask about alternating their balusters most go with something similar to the balusters in the image above. The balusters have the same profile at the base as well as the same "bead" at the top.  The major difference is, of course, is the barley twist and the tapered section in the center portion of the baluster.  These would be configured on a three baluster per tread stairway - plain - twist - plain on one tread and then again - plain - twist - plain on the next.  On a two baluster per tread stairway the balusters would simply alternate - plain - twist on one tread and then plain - twist on the next tread.
These balusters are made of poplar to be painted.