Best input/ exhaust placement?

I plan on using 2 pc fans in a small cfl grow box setup. One fan will be the input fan, and the other the exhaust fan. I am wondering if it would be better to have the two fans on opposite ends of the box, or to haave them stacked vertically with the input fan near the bottom and the exhaust fan sucking hot hair out of the top.

I feel stacking the fans would do better for temp reduction, having on opposite ends would be better for moving fresh CO2 in.

actually both/ - exhaust fan at the top and input fan on opposite side at the bottom.

i would put the intake on one side at the botom and your exhaust fan at the top. heat rises and you want to expell that heat so you can keep you temp regulated.

Thanks much to both