Is a turbo charger or supercharger better?

It really depends on alot of things...

1. what vehicle, make/model/year you are looking to "boost"

2. how much you want to spend and who is installing it.

3. how much power you want ,what type of power your looking for. ( where it occurs)

1 & 2. Alot of vehicles, either only have turbo kits avail. or only supercharger kits. If it came with a turbo from the factory/ or had a turbo model avail. That would the cheapest/easiest way to go. Alot of "popular models" have both avail.( examples: mustangs, 350Z, corvette etc.) Custom "one off kits will get too expensive fast". Centrifugal supercharger kits are "usually" cheaper and easier to install ).

3. Everyone always wants "alot", If the vehicle is stock, adding 6-8psi is usually safe. Screw/roots superchargers are #1 if you love the install throttle response or low end torque. They are more eff. at low boost levels usually <12psi, whipples are rated up to 30psi but eff. will drop usually down to 60%. Hood clearance can be a problem with this type. They will drop fuel economy more than the other, but not too bad if it has the bypass valve is installed( it let the air bypass the roots during cruising.)

Centrifugal superchargers are cheaper, more eff. / easier to package than roots/screw chargers. The downside is that they have a linear boost. (I.E. 1 psi at 2000-2500rpms, 3psi at 4000rpms, 6psi at 6000rpm ) The other is belt durability/slipage. This can be partially fixed by using a BOV and overdrive it( use a 14psi pulley, and let the BOV limit the high end pressure back to the 6-8psi)

Turboes setup for a non turbo car, is usually the most expensing, but the most versitile, with options like boost per gear program, adjustable wate gates, the availability of using multiple turboes, plus there are about 20times more turbo sizes avail. than superchargers to more fit your needs. Getting used turboes from factory turbo cars from the junkyard can save you alot of money. Turbo kits can be made to give low rpm boost/torque, but they will limit topend power because of the size of the turbo/turboes. You need to choose where you want the power, If you want 20psi/high HP don't expect 20psi at 2000rpms. With todays turboes, full boost by 2500-3000psi is can be expected for street kits (6-12psi). Cruising at 1200rpm in high gear, you will get turbo lag, but throttle response at/above say 3000rpms, the response will be there.

The real deciding point is low end torque and the sound. Some people love/hate turbo whistle or supercharger whine.