Is it more efficient to have the air condition evaporator coil place in the attic of the 2nd floor of a two story home or have the evap. Coil place in the attic above the first floor and then run the duct up to the 2nd floor and down the 1st floor? I was told that it is more efficient for the evap coils that service each floor should be above the ceiling for the floor they service. Is this true?

It does not really matter which attic you put the evapoator coil in, but the installation using the least amount of duct would be the most efficient.

Hot air rises cold air falls naturally. Actec is correct. Insulation and short duct runs will determine the best location.