[rez333]

I found this information on the net which answers all my questions (finally!):

Cost
The cost of supercharger and a turbocharger systems for the same engine are approximately the same, so cost is generally not a factor.

Lag
This is perhaps the biggest advantage that the supercharger enjoys over the tubo. Because a turbocharger is driven by exhaust gasses, the turbocharger's turbine must first spool up before it even begins to turn the compressor's impeller. This results in lag time which is the time needed for the turbine to reach its full throttle from an intermediate rotational speed state. During this lag time, the turbocharger is creating little to no boost, which means little to no power gains during this time. Smaller turbos spool up quicker, which eliminates some of this lag. Turbochargers thus utilize a wastegate, which allows the use of a smaller turbocharger to reduce lag while preventing it from spinning too quickly at high engine speeds. The wastegate is a valve that allows the exhaust to bypass the turbine blades. The wastegate senses boost pressure, and if it gets too high, it could be an indicator that the turbine is spinning too quickly, so the wastegate bypasses some of the exhaust around the turbine blades, allowing the blades to slow down..
A Supercharger, on the other hand, is connected directly to the crank, so there is no "lag". Superchargers are able to produce boost at a very low rpm, especially screw-type and roots type blowers.

Efficiency
This is the turbo's biggest advantage. The turbocharger is generally more economical to operate as it as it is driven primarily by potential energy in the exhaust gasses that would otherwise be lost out the exhaust, whereas a supercharger draws power from the crank, which can be used to turn the wheels. The turbocharger's impeller is also powered only under boost conditions, so there is less parasitic drag while the impeller is not spinning. The turbocharger, however, is not free of inefficiency as it does create additional exhaust backpressure and exhaust flow interruption.

Heat
Because the turbocharger is mounted to the exhaust manifold (which is very hot), turbocharger boost is subject to additional heating via the turbo's hot casing. Because hot air expands (the opposite goal of a turbo or supercharger), an intercooler becomes necessary on almost all turbocharged applications to cool the air charge before it is released into the engine. This increases the complexity of the installation. A centrifugal supercharger on the other hand creates a cooler air discharge, so an intercooler is often not necessary at boost levels below 10psi. That said, some superchargers (especially roots-type superchargers) create hotter discharge temperatures, which also make an intecooler necessary even on fairly low-boost applications.

Surge
Because a turbocharger first spools up before the boost is delivered to the engine, there is a surge of power that is delivered immediately when the wastegate opens (around 3000 rpm). This surge can be damaging to the engine and drivetrain, and can make the vehicle difficult to drive or lose traction.

Back Pressure
Because the supercharger eliminates the need to deal with the exhaust gas interruption created by inserting a turbocharger turbine into the exhaust flow, the supercharger creates no additional exhaust backpressure. The amount of power that is lost by a turbo's turbine reduces it's overall efficiency.

Noise
The turbocharger is generally quiter than the supercharger. Because the turbo's turbine is in the exhaust, the turbo can substantially reduce exhaust noise, making the engine run quieter. Some centrifugal superchargers are known to be noisy and whistley which, annoys some drivers or makes some very happy!

Reliability
In general, superchargers enjoy a substantial reliability advantage over the turbocharger. When a a turbo is shut off (i.e. when the engine is turned off), residual oil inside the turbo's bearings can be baked by stored engine heat. This, combined with the turbo's extremely high rpms (up to 150,000rpm) can cause problems with the turbo's internal bearings and can shorten the life of the turbocharger. In addition, many turbos require aftermarket exhaust manifolds, which are often far less reliable than stock manifolds.

Ease of Installation
Superchargers are substantially easier to install than a turbos because they have far fewer components and simpler devices. Turbos are complex and require manifold and exhaust modifications, intercoolers, extra oil lines, etc. - most of which is not needed with most superchargers. A novice home mechanic can easily install most supercharger systems, while a turbo installation should be left to a turbo expert.

Maximum Power Output
Turbos are known for their unique ability to spin to incredibly high rpms and make outrages peak boost figures (25psi+). While operating a turbocharger at very high levels of boost requires major modifications to the rest of the engine, the turbo is capable of producing more peak power than superchargers.

Tunability
Turbochargers, because they are so complex and rely on exhaust pressure, are notoriously difficult to tune. Superchargers, on the other hand, require few fuel and ignition upgrades and normally require little or no engine tuning.

And a response:

Allow me to parlay some of my knowledge then.

Cost: Brand new, yes a turbo kit and a supercharger kit will cost the same(ish. Turbos will probably be a few hundred cheaper becase there is more demand for them. Also don't forget about labor). If you have the knowlegde to build a junkyard turbo setup, then it will be much cheaper to go that route. If not, it all depends on what deals you find.

Lag: Lag is only a problem when you have a huge turbo and a tiny engine. A turbo that is sized for a small displacement engine should not suffer from any lag. A good, street-designed turbo kit should not have any turbo lag. Avoid kits that advertise "drag racing, huge power, high-boost, etc." Those will have big turbos and big lag.

Efficiency: If every turbo was built the same as Garrett's Disco Potato, this wouldn't be a problem. Sadly, most turbos were last redesigned in the 1970s. If you want to know more about the Disco Potato turbo, I can tell you, but that is mostly a Nissan Silvia turbo. And rather expensive.

Heat: Compressing air heats it up, so both types of compressors will heat the air coming into the engine. However, because a supercharger is less efficient it will actually heat the air more than a turbo. Many SC kits actually have a tiny air to water intercooler sandwiched between the compressor and the intake manifold. This only holds true for a Roots SC (commonly seen on Top Fuel dragsters). A centrifugal SC can use a standard air-to-air intercooler like a turbo, because it compresses air more like a turbo (and can be mounted anywhere in the engine bay). However most Honda SC kits I have seen use Roots-type superchargers, which are also prone to heat soak. So they will lose power as they heat up. Also rememer that SCs tend to run lower boost than turbos. Typical SC kits run about 7 psi. Typical turbos run about 8 or 9 psi. Suffice it to say that turbos will run cooler pound for pound. Also, you may need to upgrade your cooling system, no matter which route you take.

Surge: True if you have a late-spooling turbo. However, if you keep out of the boost, you can actually drive around town like your car has no compressor at all, saving gas mileage. That's not possible with an SC.

Back pressure: Both types of blowers will benefit from a bigger exhaust. However, the turbo will make better use of that flow because it can suck air out faster. Think about it like this: what's easier, pushing a column through a hole, or pulling it out? Turbos pull, SCs push.

Noise: BOVs can be very loud. But it's a cool sound. And again, if you keep out of the boost, you won't hear it. My Silvia has a 3.5" exhaust, and a fat turbo, but the loudest part of the car is the blow-off valve. Around town, the car is actually quite civilized.

Reliability: Both compressors will reduce the life of your engine. Simply put, it wasn't meant to take it. The oil bit is true, but only if you drive like an idiot and immediately shut off the car. If you've been racing, then allow a brief cool-down period (five minutes or so idling, or about ten minutes of sane driving). On the street, oil-clumping should be a non-issue. Also, if you run your turbo within it's design limits, then it will be fine (ie no overspinning. Turbos can over-rev too) Any off-the-shelf kit will already have this worked out. But like any part turbos (and SCs) will wear out. As for the manifolds, most turbo kits use cast-iron exhaust manifolds, which are very strong. Tubular manifolds, seen on race cars, are weaker and less reliable, but only in cars where there is a lot of heat. You won't need the extra flow offered by the tubular manifold unless you are doing some hardcore racing.

Installation: This is pretty much correct.

Power output: Also corect. This is because at a certain point, the SC takes away more power than it actually produces. There is a plateau where turning up the boost on an SC causes a power loss, because the engine can't overcome the drag losses caused by the SC. Also, changing the boost on an SC means changing the drive pulley. On a turbo, it's a simple push of the button or a turn of the screw (if you have an external wastegate).

Tuning: This is only true if you have a muscle car. Most import tuners are much more familiar with turbos and can tune them fine. And with the invention of electronic boost controllers, boost spikes are a thing of the past. Computers have made turbos the compressor of the future. Changing the the boost is a matter of telling the computer to change the ignition timing, add more fuel, and turn up the boost. Any competent tuner can do that in about 5 minutes. To do the same with an SC means replacing the boost pulley and then retuning. That's at least 30 minutes.

A low boost turbo in the long run will probably be your best bet since more people are familiar with the mechanics behind them. Plus parts will be a bit easier to get (if you blow a turbo, you can probably replace it with something from a Mitsubishi Eclipse). Also, the BOV will make that cool sneeze everyone loves and a grinning intercooler just looks freaking cool.

My one question is, why do you want to add more power? Just because? With today's gas prices, your money may be better spent on some bolt-on parts, which when combined well can give you about 30 hp and a very nice sounding car. Plus the reliability will be much higher and the initial cost will be lower. Plus it will be easier to inspect the car (assuming you have to pass an emissions test where you live).