Who to address on the cover letter?

I address all cover letters, letters of rec, etc. "Dear Committee Members:" Don't waste your time addressing it to an individual. The only thing you can achieve by doing that is embarrassing yourself and giving the search committee the chance to have a good laugh at your expense. If you do it correctly, it doesn't actually achieve anything; why give yourself one more thing to stress about?

The advertisement usually specifies to whom the application should be sent. In such cases, use the name that's listed in the advertisement. If no name is given, then I would vote for the first option, as it is the most inclusive.