best? theres no such thing as the best, its more a matter of what type you want for whatever application, there are centrifugal and positive displacement types and within positive displacement there 2 variations.
centrifugal's (vortech, paxton, pro-charger) make most of their power high in the power band, while the positive displacement (roots/twin screw) make it in the lower to mid range. (the 03 cobra uses a roots type)
actually theres too much info for me to give you in this little box so ill provide you with a link to a great explanation of both, the articles here are extremely helpful and taught me alot.
http://www.superchargersonline.com
look towards the bottom right of the page under messege forums, the articles are called superchargers A-Z.
enjoy the info!
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1995 Mustang GT 5.0
BBK CAI, Pro-M 75mm MAF, Pro-M Optimizer, BBK 70mm TB, GT-40 Intake, 24# Injectors, AFR 165's, 1.7 Roller rockers, Crane 2040 cam (E-303) BBK Equal Length headers, BBK O/R X-pipe, Flowmaster American Thunder 2 Chambers. FMS 3.73 Gears, Lentech AODE 2800 stall, BBK 255lph Fuel Pump, BBK Fuel Pressure Regulator. MSD 6AL, Steeda UDP's, FMS Aluminum drive shaft, Autologic chip Larocca tune.
Best Supercharger??? 
