When I was a teenager, I worked at a 10 minute oil change place... One of my coworkers saw a demonstration at a car show where they compared STP to Motor Honey by putting them in a bowl and using a kitchen blender... The STP went so far up the beater of the blender where the Motor Honey climbed up the shaft...
So I lean toward the Motor Honey if I have a choice, but STP will still do the job....