Out of Stillen, ATI, Vortech, HKS, I picked Vortech. It seemed to be the best all around kit. The Stillen is very reliable, but gives you a little less power, ATI is a nice kit and has a lots of potential to be upgraged, but has no timing and fmu solution that comes with it, HKS seems to be great but its a little $$$, would rather go TT, and they say its not recommended to have any mods on your car. Vortech is showing nice gains, not to loud, has a ECU piggy-back that solves timing and FMU problems ( pretty much a compleat kit) Pretty safe for the car if you keep it a stock boost.
my 2cents