04 corolla s, what to do!

i got a 04 corolla s grey w/ spoiler, i'm gonna get flowmasters because exhaust expert says they're the lowest sound i can get. should i get short ram air or cold air intake, with gas mileage in mind. i heard cold air reduces mpg, does anyone know? I own a modulator but don't know about if i want to install it for fear of damage to engine. answers to concerns and tips for what to do to it very appreciated.

The intake works very well. I have the short ram air instead of a cold air, due to the fact that I was afraid of getting in wet during the monthly rain storms I have in my town. It really does increase gas milage. I don't know what to tell you about the modulator. I don't really know what that is.