Which way should a down stairs ceiling fan be turning to work best with AC?

A fan blowing in any direction will circulate the air, but for best efficiency, a reversible fan is best. Cold air drops, so a fan pulling up will circulate cold air better, cooling the ceiling too. Hot air rises, so heat should be used with a fan blowing down to heat the floor.

We are using this system in our new house that we are building.

As far as the AC is concerned, it doesn't matter. Either direction will circulate the air.

For you to feel cooler with a higher thermostat setting most people like for the fan to blow down because you feel the breeze from the fan more.

I personally don't like the "drafty" feel of the fan blowing down so we have ours blowing up. You still feel a bit of air movement but it is softer.

If it's turning in the direction that the side of the blade that is pitched down hits the air first,then air is pulled up.

If it's turning in the direction that the side of the blade that is pitched up hits the air first,then air is thrown down.

Up!! on any floor. Cold air falls and hot air raises.

Try it both ways and see what works for you.