Is It More Appropriate To Use "One" or "You" When Speaking Of An Indefinite Person?

In high school English, it was imparted to us that in formal American English when speaking about an indefinite party, we should use the word one. For example, "One should cover his or her mouth when he or she has to cough". This seems a bit stilted and awkward--before this instruction was given to us, I believe most of us would have used you--"You should cover your mouth when you have to cough." In formal and business writing, which word should one (or you) use?

Both are fine, but the second-person you sounds more direct and thus less polite than the third-person one — almost like an order as opposed to a hint.

If I wanted to both use you and sound polite, I would go with the simple alternative:

Please cover your mouth when you have to cough.

Lastly, if you need a shorter alternative for the rather cumbersome "his or her" and "he or she", there's the singular "they".