What are the key features to consider when choosing a mountain bike headset?

When choosing a mountain bike headset, key features to consider include the type of headset (threaded or threadless), the material it is made of (aluminum, steel, carbon), the bearing type (cartridge or loose ball), the stack height, and the compatibility with your bike's frame and fork. These factors will affect the performance, durability, and compatibility of the headset with your mountain bike.