I'd go with the ABS. Copper is a good material, but I dont like using it for drains unless I have to. Certain things that are put down drains can be corrosive to copper. I install alot of cast iron drainage, but this is in commercial buildings where fire codes require it. Cast iron can and will rust on the inside causing "hills and valleys" and rough spots where clogs can and do occur. On the up side, cast iron is extremely quiet. Plastic, whether ABS or PVC is my material of choice for drains, wastes and vents (DWV). The walls are smooth, resistant to corrosion from alot of chemicals and food acids (think citrus...I've seen lemons from a bar put holes in copper drains) and when installed correctly will outlive both you and me.