The hiring manager, not HR. You'll get priority from HR if you do that. At least, that's the way it worked when I worked for HR.
There was a little checkbox in the database for that in our database after I scanned in the resume. That checkbox insured the resume would appear on top of the other resumes with the hiring manager. The paper copy would also be placed on top of the stack because of that as well.
Whether digitally or on paper, we always made sure that the hiring manager could find the resumes of the people he knew first. This was to insure that hiring managers couldn't accuse our department of losing/filtering a particular resume.
To this day, I won't apply to a job without knowing the name and email address (or mail drop) of the hiring manager first and I always send my resume to the hiring manager first, even if he/she doesn't know me. Perhaps, there is a small delay because of that, because I'm sure the hiring manager just forwards it HR, but I feel much more confident doing that because of what I've told you.