Open windows or A/C for best mpg?

[seonadancing]

Here in our country where it's usually around 35C, I keep it a point to put the windows down when i'm the only one in the car. Since i have window visors on, I open my window only slightly lower than the bottom of the visor so i can have some air and at the same time, more engine power.

[hex]

I watched an episode of Mythbusters once and they did a test on this. Having your windows down produces drag. However, they did most of their testing on highway speeds, so if you're driving on the main roads, I would probably just roll the windows down.

[Super Mario]

Around the city I cruise windows down. On the freeway it's usually cracked so that the windows are still under my visors, or A/C, depending on whether or not I'm going uphill.