Assuming both SCīs and turbos are done by professionals and reputable tuners (and this is a huge if), turbos will generally yield higher pressure and more power but are much more difficult to install (cooling must be massively increased and engine internals generally must change for low compression) as well as more difficult to calibrate. The end result may be better with turbos but because of the above, also more expensive! I will say that one advantage of SCīs is higher low end torque and no turbo lag. Depending on how powerful your car ends up being, turbo lag may not really matter since you canīt put all that power down to the ground effectively anyway.
Try Mosselman Trubo systems as well, they may have an SC system out just about now and are working on a turbo kit.