We have 10 mic stands to lug around to gigs, and they keep destroying various bags we're tried, so we have invested in this Gator Bag. It's quite an expensive way of carrying mic stands around, but we have been impressed by its quality and stength. It only holds three stands, but it's generous proportions mean we can carry extra items in the bag (mic clips, goosenecks, etc), so we'll probably buy two more for the rest of our stands (which must mean I'm impressed).
I suspect 3 stands per bag is sensible so that you can lift them easily, and you don't have to take all the bags if you only need half-a-dozen stands.