Hi Bill,
I'm convinced edge grained osage makes the best BBOs. By orienting the grain this way you minimize the use of the soft, punky earlywood in compression and utilize the latewood efficiently/evenly. But, as Mike and Eric mentioned, you need clear wood to do this. If you have pin knots they will likely run acros the limb, collapsing faster than the surrounding wood. If they are on the surface of the belly, they can ruin a bow if you're not careful.
I've never made an edge grained osage selfbow before, but would recommend backing it with rawhide or something to prevent splinters. With that said, edge grain hickory makes swell board bows.
Good luck and let us know how it turns out!
MG