David Gaskin

I guess it should always be superchargers as their power output is more even balanced throughout the rev range. A turbo only cuts in when above a certain RPM and than kicks in all at once. As BigAl says though Turbos are probably cheaper and the reason why they are more common. I am unsure which is the most reliable but I do know that a WW2 Spitfire used a supercharger so that make it a winner for me... :)