Are you supposed to use one in certain configurations and another in the other? Or is it just “try both and see which you prefer?” What characteristics would one have over the other during use?
The one marked + is simply thicker, placing your eyes at a slightly further distance from the screens. You just select the one that is more comfortable.
I based my choice on the fact that I am using prescription lenses, so I picked the thicker cushion to keep the lenses slightly further from my eyes. If you’re not using prescription lenses, then I would probably stick to the thinner one.