You will most likely get more than one opinion on what ammo to use. The following is one person's opinion for .40 S&W.
180 grain jacketed hollow points or the 135-155 grain jacketed hollow points by Cor-Bon, Winchester, Federal, CCI or Remington. All are good stoppers, but the lighter weight bullets have the best stopping power records on the streets.
The real-world shooting database clearly favors the lighter 135-155 gr. JHP loads. I personally would carry the potent Cor-Bon 135 or 150 grain jacketed hollow point or the Winchester Silvertip 155 grain jacketed hollow point (X40SWSTHP). The 135-155 grain JHP kicks less and has higher kinetic energy and stopping power than the 180 gr. JHP loads. The 135 gr. JHP appears to be a real stopper.