It is for me essential to have a very good braking.
The caliper brakes
The most basic mountain bikes usually have stirrup braking. This is the classic braking. I think it's not good enough when you have dogs shooting in front of you.
Mechanical / hydraulic brakes
But more and more, we find the possibility of having mechanical or hydraulic brakes, disc brakes.
I encourage very often to take hydraulic brakes because they are particularly effective. And when you have wild dogs in front of you who think only of one thing: go for it! Well it's not bad to be able to maintain some control with effective brakes.