Stock.
Stock it comes with a cold air intake. Intake leads away from the engine, towards the bumper, to draw in colder, denser air.
In fact, this is standard on almost all vehicles.
So, while you can get a shiny chrome aftermarket one, it won't do a thing for the car, that the car doesn't already have.
Generally speaking, you gain 3-4 horsepower near redline. Basically no gains during the rest of the power band, and usually a loss in low end torque.
So, unless you want peak numbers, and don't care that the car is slower....leave it stock.