When I print full frame I use a glass carrier or purpose-milled full frame carrier. I can't stand raggedy borders, but I think an ultra clean, 1-2mm black line is really sexy on b/w prints.

I eschew them when I crop ever so slightly to correct a crooked horizon, but if it's part of a series of printed work, I will make a mask the size of the image area and burn the line in with white light from the enlarger.