Simple answer is that almost everyone shoots steel shot -- bismuth, tungsten matrix, etc is simply too expensive. You can buy great steel loads (12 gauge, 3 inch) with 1 1/4 oz steel shot in #3 or # 2 shot which is very effective on ducks out to 40 yards -- we use # 1's or BB's on geese -- I live in south Louisiana and hunted 9 days of our 16 day teal season this year and have made approx 20 duck/goose hunts this regular duck/goose season (for example, hunted 23 December with a friend and we limited on ducks - 7 teal, 2 pintails, widgeon, 2 grays plus 4 speckled-belly geese; and on Christmas day with 3 of us in the blind, limited on ducks -15 teal, 3 mallards plus 3 specks, 1 Canadian, 1 blue, 1 snow)
Steel shot works well as long as you place the pattern on the bird.