For larger work, I use a wooden "french bevel" that is integrated into the framework built into the back of the panel.  For smaller work, I use an aluminum "Z clip" cleat hanger.  For the heavier work, one half of the wooden french bevel needs to be screwed into a stud in a wall.  For the smaller/lighter work, thin nails are sufficient for firmly attaching the Z clip to a wall.

I prefer to use a french bevel or Z clip because they make it easy to properly orient this work.  All you have to do is use a bubble balance to make the french bevel or Z clip level on the wall, and then when you place the artwork on them, the artwork will be properly alligned.