Its hard because the metric will change based on your need. When the shop is was slow I focused on transactions per day when the shop was busy I focused on hardware turnover and carried what was moving the most. Focusing on gross product margin with nobody walking through the door is a bad idea.
Assuming the store is busy I would want to see what is moving. Many times I was about to cut a product because I thought it was not popular only to find out its been a very quiet stable mover.