Whichever SP shoots best out of your rifle at 100 yards. If you're not reloading, you'll have to try a box of as many brands as you can to find the ammo that shoots best out of your rifle. Assuming it's an SKS or Mini-30, it'll have to cycle the action too.
Most of the ammo makers load 123 or 124 grain SP's. Cor-Bon loads a 123 Barnes TSX and a 150 SP, but they're expensive.