Light picks are great if you wanna learn how to alternate pick faster on a string to build speed, but they are really bad picks to play leads with. Of course, this is all on preference to the player, but leads are much better played with a heavier pick. This doesn't mean you have to go 3 mm like alucard, he just prefers them, but the heavier the size of the pick, the better it is to sweep and the better clarity that you get from alternate picking a pattern. Overall, heavier picks is the way to go, since it's sturdy and won't flap on you. Also, it's much better to use for artificial harmonics.