How "Green" is a Prius? in re batteries and mining?

I saw an article in a paper (IBD I believe) that questioned the footprint of the Prius (and other battery cars) due to the pollution caused by the mining and the smelting of the nickel. I know it's close to earthday, so what's better a hybrid or a high mileage gas engine? Pls weigh in on diesel engines if you know what UR talking about