I always center the image on the paper. I don't feel the various conventions about centering the image in a mat board for display hold up well when hand-holding print to view.
What is your technique for centering the image on the paper? I've got a four-bladed easel from LPL that has these pre-cut scores in different sizes, but they generally don't line up very well with the placement of the image when using the rulers on the blades to set the image size.
"Art is is a picture of some dude I never met smoking under a lamppost at 6400 ISO and in BW."