A 30t shackle with a bolt and nut is just as strong as a 30t shackle with a screw pin.  The only reason to prefer one over the other is if there is a reason you do or do not want the pin to be able to turn.    The pin diameter should be the same either way.   Screw pins are generally used for things which have to be taken apart frequently, while bolt type is more likely to be found in a permanent installation.