Honestly, the kryponite shard came in handy the most for batman, so I'd go with that. Honestly, out of the Pantheon of Heroes and Villains, almost everyone is affected by kryptonite, though humans need prolonged exposure to get cancer. But, I remember one story where Superman is shot by a kryptonian bullet, and batman saves him by using either the kryptonite shard, or a scalpel he made from it, I can't remember which.