This Old House: It all depends on the vibe, some people want expansion and contraction and make the interior feel older and less perfect. So depends on what fits your need. We mostly do fresh clean shiplap, nickel gap or 1/4". WE do it in MDF of poplar wood that should be very stable. I've never done it in cheap pine (DIY'ers do all the time to keep cost down). Our builders always pre prime all the boards and even one coat of finish before installing too. That way once installed they get one coat and if the boards move around to expand and contract you won't see unfinished wood! All the cost is in the prep!