1) Parking on asphalt (black-top) is the best since it won't leach out the petroleum products (as quickly) in your tires.
2) Parking on concrete is ok, but it will leach out the petroleum products in your tires quicker.
3) Parking on gravel lessens the change of leaching, but increases the chances of parking on a sharp rock or an errant nail.
4) Parking on wood leaches out the petroleum products on your tires faster than concrete or gravel.
5) Parking on grass or dirt greatly increases the petroleum leaching.
Go with the black-top asphalt!
Hope this helps,
WoodGlue