346 Stainless steel picks are the top for durability and the bright and cutting tone. Comes in triangular shape and in 0.70 mm gauge. 346 Brass picks are long lasting and will give you that classic tone. Comes in triangular shape and in 0.70 mm gauge. 346 Copper picks are brighter as well and produce a warmer tone. Comes in triangular shape and in 0.80 mm gauge.
In general, the harder the pick material the brighter and more biting the tone produced. A problem with metal picks is that they tend to damage a while the surface of pick guards, fretboards and guitar tops.