I am of the opinion that running the grain parallel to the LEADING EDGE is the best plan. It allows for the easiest "roll" of the skin around the curvature of the airfoil while still providing good longitudinal stregth to the wing. Also, whatever method you choose, use the same angle on top and bottom, otherwise you may induce an unwanted twist. The type leading edge you describe (somehwat like a P51 Mustang) can be skinned in this fashion but add another piece to the skin that is skewed to the leading edge at the wing root. I also like to put spars in a foam wing. Use a hot wire to cut a groovetop and bottom, then place the spars in it with Gorilla Glue. Sand off the excess expanded glue before skinning (See other articles about using PU glue for skinning). Use same technique for placing gear blocks or servo boxes before skinning.