the inside, of course.
Invariably the side that hits the floor.
The side that is opposite the counter, you know the side facing up, the side that will land down when the bread is neatly and completely butterd and falls off the counter to the floor.
The side that has been up a butt crack
I hate butter
The outside usually.....
the palm of my hand...
The matte side, the butter slips off of the glossy side.