[Dadhawk]

If I were to add one, it would definitely be a Supercharger, primarily for simplicity and the bottom end (off the line) boost. I don't particularly care for the "turbo lag" boost at a certain RPM, I want my power off the line from the beginning.
It seems that one of the biggest complaints about the 86 is just the thing a SC provides some correction for and a TC would exaggerate. To me a TC actually creates the "lag" in other cars that people complain about in the FR-S.
That said, there are definitely advantages/disadvantages to both, and you have to figure out which one best fits your style. Since mine is a daily driver, I want the off-the-line kick in the pants.