Either or doesnt really matter. Our stock intakes are pretty good.

 

Fuel milage, easy keep the air filter clean. Keep the tires inflated and run 5W-30 synthetic (not high milage and possibly 5W-20 if you are adventurous.). Then if you run champion spark plugs change every 10K or 20-30K with NGK.

Then drive sanely and brake only with the right foot if you have an ATX and keep spacing around you good.

 

The biggest bang for the buck in fuel economy is almost always to choose the tires with the lowest rolling resistance and to run these tires slightly higher in air pressure. Consumers Reports magazine is the only organization that presently reports tire rolling resistance, although their is a law pending in Congress to make the tire makers publish the resistance. Tire rolling resistance also goes down as the tread depth wears away.

Pirelli is one of the few companys that provides a little information on tire rolling resistance:

http://www.us.pirelli.com/web/techno...e/default.page

Adventurous? Like to find out for yourself?
You can test your own vehicle aerodynamics and tire rolling resistance with the Java calculator stored on this archived web page originally created by race-technology company for their AC performance meter (like a G-tech) but still in the Google Wayback Machine:

http://web.archive.org/web/200408030...DownCalcs.html

one tip: The 'A' in the Cd x A value they calculate for you is always in 'square meters' despite you clicking the mph and pound check boxes.

Vehicles like the Toyota Prius, Honda Insight, GM EV1 and other cars went to considerable expense to get low rolling resistance tires for better MPG or electric power range.
There is a table of such tires at this weblink:

http://autospeed.drive.com.au/cms/ar...A=0952&P=3

More from professionals on tire rolling resistance and the pending law in Congress:

http://www.tirereview.com/default.as...&item=4080

 

Driver technique can considerably improve MPG in any vehicle.
Skilled drivers are called 'Hyper-Milers'
Here is an article on Wayne Gerdes, a well-known HyperMiler:

http://www.motherjones.com/news/feat...permilers.html

Here is a husband/wife team of HyperMilers sponsored by Shell Oil:

http://www.scoop.co.nz/stories/SC0601/S00020.htm