Anything you can put where it counts, whether hardball or super duper HP self defense ammo. I carry Speer Gold Dots in my LCP because local law enforcement uses the same ammo in their weapons.
But something to keep in mind, hardball rarely jams compared to hollow points all else being equal.
"Well, your honor, he didn't use anything different than the police use." This as an answer to the prosecution's charge of using mushrooming killer rounds.