SC's sound awesome.
The reason SC's are generally considered better is that the CTR is FWD and already puts out 200bhp, if you turbo this all through the front wheels and with the extra torque you get from a turbo all of a sudden will cause traction issues. Thats not to say that its not a good mod as many people in teh past have turbo'd a CTR with great results.
IMO a turbo'd car is better suited to a AWD vehicle and chassis.
The plus' of a SC are that teh power delivery is much more subtle and progressive, instead of getting a hike of like +100ft/lb of torque between 5 and 6K rpm you get it over the whole range and the car will pull better over the whole range, and ultimatly the car will put the power down better through the front wheels. Also dont forget K20's are a very rev happy engines so having something that increases the power over teh full range is better than having it all of a sudden which is gerally what you get with a turbo.
Also Jackson do bolt on kits which have a very good rep and as I see it have less potential problems than with a turbo.
IF I was going FI on my K20, it would be SC and these are the main reasons.
Both of these NEED a LSD.
You will gett bigger figures on teh dyno with a turbo.