Kenne Bell kit hands down.
We've done numerous of them on the S197s.
Our most recent one went 12.02@ 118.9MPH with the 4inch pulley, which is 7-8PSI peak.
I will say this, the whipple on the 05+ does have a very clean install.
But over all the KBs run cooler discharge temps. And thus make more power and will last you longer in terms of power out put.
Another alternative is a ProCharger. Makes good power also. If your interested in a kit let me know :)