Okay, we'll lay a groundwork with some facts here.
Yes, far more 4cyl. turbo engines currently come from the major manufacturers. There are advantages and disadvantages. Turbos have no drive belt, thus no parasitic power loss. They also have more options in regards to sizing, you can put a really small turbo on an engine (VW 1.8) or a really big turbo on an engine (1989 Porsche 944T). You can also tune small displacement (re: 4cyl) turbo engines more easily to have low emissions. Be sure to read this writeup by WRX guru Mike Shields for a good explanation of the US market Subaru EJ205:
That being said, small displacement turbo engines can have significant disadvantages. Turbo lag, high rpm boost onset (i.e. no power until higher revs on the tach), cruddy throttle response, cruddy throttle adjustablilty (like an on or off switch).
I've driven the following turbocharged 4 cylinders in anger:
2.0L Mitsubishi, circa 1996
2.0L Subaru WRX, 2002 and 2003
1.8T VW, 150hp (Golf and Passat)
1.8T Audi TT(VW) 225hp
2.2T Ford Probe, 1989 (Mazda engine)
1.8T Mazda 323 GTX (1989)
2.5L Porsche 944Turbo
Of all those, the 1.8 VW versions were the most driveable by far. Minimal turbo lag, good throttle response at all RPM, and excellent power delivery from very low RPM (2000 or so). The rest all had varying degrees of turbo lag, lazy throttle response, high boost onset, etc. All made very good power though. Get the turbo on the boil, and all of those cars moved out very well. In the turbo's favor, its hard to beat the brute, high rpm power of a turbo engine. No parasitic loss, tunable compressor/exhaust housings, and monsterous boost makes turbo engines a great choice for extreme applications......i.e. drag cars or extreme road racing cars.
That being said, I'm firmly on the side of supercharging small displacement engines. Everyone knows small engines don't have much low end torque, and positive displacement superchargers solve this problem beautifully.
A distinction needs to be made here between centrifugal and positive displacement superchargers here. Superchargers like the Lysholm twin screw, the Whipple, GM roots, etc. start making boost immediately off of idle. Centrifugal superchargers like the Vortech or Powerdyne, make boost in relation to RPM: The higher the RPM the faster the impeller spins.....thus more power as the engine revs higher. They're kind of like a belt driven turbo. There isn't enough space here to break down the techincal differences, but you can tell the difference between the two by looking: Positive displacement superchargers are a big ass rectangle, and centrifugal superchargers look like a huge snail......like turbos. Sorry to the techies for such a basic explanation, but it works, doesn't it?
Centrifugals will act more like a turbocharger, increasing power as rpms go up. See the explanation of Comptech's centrifugal supercharger for the stratospheric revving Honda S2000:
Roots type superchargers, on the other hand, will make a small engine act like a large one right off of idle......Mercedes 2.3L is a great example. Another is the current Mustang Cobra. Another great example is my buddy's Kenne Bell supercharged Miata. That little 1.8 has nasty grunt right from 1500 straight to redline. A MOST impressive engine. 9psi into a 1.8 has that thing putting out 210 or 215 at the crank. Darn nice in a 2500lb. car.
On the downside, positive displacement superchargers don't tune for emissions or gas mileage very well. Boost straight off of idle requires more fuel, which obviously decreases gas mileage and certainly makes meeting emissions standards more difficult.
The big issue with me is throttle response though. Positive displacement superchargers retain most, if not all, of the razor sharp throttle response normally aspirated engines have. This is critical on a road course, where throttle adjustablilty can mean big gains in lap times.
Turbo? On the 3 forget it. That's as far as I'm concerned anyway. No way I'd give up the throttle response and all that comes with it. Positive displacement supercharger like on the Miata? Bring it on. All the power with not a lot of downside.
No way I'm bolting ANY power adder on my car without a Quaife or Torsen differential installed though. All that extra HP would be wasted in wheelspin.