What's the harshest horse bit?

I'm curious, what do you consider to be the harshest horse bit on the market? Is it a particular type of bit that's known for its severity, or is it more about the way it's used? I've heard some trainers swear by certain bits for certain behaviors, but I'm wondering if there's a consensus among experts on which bit is the most severe. Could you elaborate on your thoughts on this topic?