Rainheads

Rainhead shower heads are inferior to normal ones.  For those unfamiliar with the terminology, a rainhead is a shower that releases water straight down, as opposed to at an angle.  

If we take a look at the diagram below, we can see that there are two areas to a person's head - the area (marked by blue) where water is ok, and the area (marked by red), where water is not ok.  This is a fairly easy concept to grasp; most people don't want water and soap getting in their eyes and all over their face.  Face washing is part of a normal shower routine, but for the majority of the time, most people prefer not to be splashed in the face.

The fault of the rainhead is the angle at which a head needs to rotate in order to get water on the correct areas.  As we can see in the second diagram, there is an angle theta difference between the two types of showers.  Therefore, there is additional strain on the neck of the person in the rainhead shower.

Another takeaway from the diagram is that a large portion of the rainhead water is going unused (note the large portion on the left that does not come in contact with the head).  Besides neck strain, rainheads generally have less pressure, so it takes longer to clean yourself.