By answering this question, I'm NOT recommending that the average citizen stock up on masks/respirators in preparation for a pandemic. However, if I had a job that required potential contact with infected people or animals, IMHO I would want a respirator that was NIOSH N-99 or N-100 or European FFP3 certified. Just as crucial as the correct respirator is proper training, fit-testing, and periodic fit checks. Of course, other personal protective gear like gloves, aprons, coveralls, goggles, visors, etc. are also crucial if operating in a high risk situation.

The only situation where your average person would be recommended to wear a mask is if they are sick or starting to show symptoms like fever. In that case, the person should wear a surgical mask or better, if available. You want to minimize the sick person from launching millions of virus-laden droplets into the air when they cough or sneeze.