turbo...i agree with robert1320, turbos are not free hp, they run off the exhuast which is a byproduct of whats happining inside the combustion chamber.
the difference is, it takes less power to turn a turbo impeller than a supercharger, the supercharger is held to the revs of the motor and the ability of the motor to hold together(the more boost, the more pressure on the crankshaft since it runs off the snout of the crankshaft, in essence its slowly twisting it upwards, especially in high boost applications, on a turbo u have to worry about exhuast piping, and correctly sizing it to ur motors app...
buick grand nationals are factory turbo muscle cars, the new cobra is factory supercharged, as is the vette,but power for power, everyone would agree its a turbo, thats why all the imports are turbocharging rather the supercharging, it makes more power and is more concealable that a supercharger....perfect for sleepers.