I really liked the "head" pieces that were first used on the Roboriders and (as I recall) only in three sets in Bionicle as armor: Nui-Jaga (For the tails), Makuta Teridax (For the feet) and Keetongu (For the leg armor). They seemed to work well in a lot of different situations whether it be bodies or leg/arm armor and were very easy to find a way to attach them.