The seed side should generally face up because then you will be quilting in the same direction that it was needle punched, making quilting easier. Sometimes, though, when people know that the quilt will be used as a play mat, they put the seed (cotton) side down & the scrim side up. The reason for this is the scrim side is the tougher side & is meant to be the side that gets the most wear & tear. On a regular bed quilt, that's the back side. On a play mat, that would be the top. Personally, I always make them with the seed side up & haven't had any complaints yet but everyone is different.
