I have an Air Raid intake (intentionally NOT calling it "cold air") and it is pretty sweet. when you stomp on the pedal, you can hear it snort, then the thing wraps up, and takes off like a shot. My engine is stock, though I have dual pipes, dual cats, no y-pipe. For true "cold air" you need to port it to the outside of the car, preferrably the front, in lieu of a fog light, or on top, with an induction hood.
With the stock intake, what you gain in having cooler air coming from the wheel well, you lose a lot more in restriction. With an aftermarket setup, you do lose some by having hot air going into the engine, but then again, that's why injected engines have air intake temperature sensors to adjust the mix.
So my vote is for an aftermarket intake.