Turbocharging gives you more mid-and high-end gains, while supercharging gives you more low-end grunt. A huge turbo could probably produce more power than an equivalent blower, but the power curve of the car will be peaky towards the top of the rev-band. Superchargers are nice because you can increase their gains [in one instance] by changing a pulley. Which is better? Depends on where in the rev-band you need the power.