Agreed that Doug fir is quite tough and makes a good stumping arrow. Hardwoods like ash, hickory, maple are tougher still, but are usually a little physically heavier than I like to shoot. I don't stump with bamboo often, but can't remember ever breaking one. It just may be the toughest stumper.
In fact, I do most of my stumping with old POCs. I take DQ's advice. I don't fall in love with them because I usually don't have them that long. I do use a lot of reparrow footings to give shafts broken off behind the point new life.
I don't use carbons for stumping, even footed carbons. Footed carbons, particularly if the inserts and footings are epoxied, are real tough, but it just hurts/costs so much when I break or lose one.