Is it best to breathe out through the mouth?

Answer 1

Breathing through your mouth means you take in more air at a time, if you're running it can be a good method for breathing. However, with breathing through one's mouth you don't get the filtration that's given by breathing through your nose, "nose hairs" cilia work as tiny filters to help keep gunk out of your lungs, the mucus housed in your nose also helps with this.

I recommend breathing through your nose over your mouth, while your mouth takes in more air at a time, you're more likely to catch a cold or bacteria(or dust, spit, etc.) in your mouth than you are in your nose.