What greeting should I use in a cover letter?

Recently, a client contacted me with the following question, "If you are unsure of the hiring manager and only have the HR email and/or address of the company, who should you direct the cover letter to?" My response was that in situations like this, I address the letter to "Dear Hiring Manager." Another option is to contact the company and ask the administrative assistant; however, for larger companies the administrative assistant may not have the inside scoop on all positions. Therefore, my recommendation is to use "Dear Hiring Manager" to ensure no mistakes are made.