That's strange- I've always heard that turbo's are considerably less reliable than superchargers. It's true that most of the time you'll make more power with a turbo, but in doing so you lose bottom end torque.
Superchargers tend to be more efficient than turbos and it generally runs in this order (least to most)
-Roots Blower (NOT EATON TYPE)
-Turbo or centrifugal supercharger
-Modified Roots Blower (like eaton with the slightly twisted rotors)
-Screw type Supercharger (Lysholm Supercharger)
Although they are difficult to find (1 or 2 companies in Australia importing them) the screw type is the best option. They give a MUCH flatter boost curve than any of the others and don't heat up the air as much or take as much power from the crankshaft.
To put this into perspective, simply swapping the Eaton supercharger for a Screw type of equal disp/rev will produce a 40hp increase in the supercharged Jaguar XJR/XKR motors.
There is another interesting advantages to superchargers, one which isn't immediately obvious. In off boost conditions, they still heat up the air, thus giving a lower density charge to the engine and so improving fuel economy.
Some good reading: http://www.jagweb.com/aj6eng/supercharging_article.html