Honestly, it's personal preference. Some people like a bigger grain broadhead because there is more weight, and more of a shock when it hits the animal. I use 100 grain and that's because it's what i feel is best for my bow setup. Also it depends on the game. A lot of bigger game needs a bigger grain broadhead to get more of a shock on such a big animal. I hope this helps a little. If not im sure someone else can explain it better.