Do you crab or forward slip in X wind landings

Side slip is the easiest and most powerful form of crosswind correction. Simply use the rudder to keep the nose of the glider parallel to runway center line and lower the upwind wing enough to counter the wind. To much bank and you drift upwind of centerline. Side slip can be maintained all the way to the end of the roll out just by keeping the upwind wing low. If the cross wind is to strong for this method you shouldn't be flying or you should select a different runway.

Crab Requires a transition to a side slip just above the ground and almost guarantees a side loaded landing either from kicking to late or to soon and not getting into the side slip quick enough.

Forward slips are not really for crosswind correction they are more for glide path control.