Based on my experience - which is all I can talk about - I'm usually out of the door quicker when I self-check than when I wait on line.
Maybe it's just my HD, but there's usually at least one self-check station open when I walk up but usually more than one person on each cashier's line.
When there's not, I use a cashier, which is often quicker than doing it myself - if there is no line. I can scan my card while (s)he's scanning items. By the time (s)he's done, all of my info is in the computer.
I don't mind paying the same price at both stations as long as I have options for getting out of the door faster.