A few things learned over time. Always test any new gun by making sure it will fire at least 200 consecutive rounds without any failure. With an auto pistol, that is 200 consecutive rounds with each carry magazine and with the carry ammo. I have known cases where the cheap practice ammo worked perfectly but the expensive carry stuff failed. In one case, the gun owner had not fired the high price stuff because it was too expensive. Fortunately he learned of his error on the range, not the street.
Sure that is a lot of ammo, but those who cheap out just don't get it. The idea is not to show off macho by carrying a gun, it is to save your life. So how much is your life worth? If no more than a cheap gun and bargain ammo, forget the carry; you are not worth it.
Avoid the latest and greatest gun/ammo. Rely on a gun and ammo with a proven track record. Sure any individual gun could be a lemon and any brand of ammo can have a dud. But that gun that came out last month is more likely to have bugs than one that has been on the market for 30 years. Same with ammo.
Everyone scorns FMJ bullets, and all the gunzines get ecstatic over that great new expanding bullet; but that bullet can't expand in a bad guy if it is hung up on the feed ramp and that funny feeling in your stomach is a knife going in and being twisted. Unless I have thoroughly tested some exotic bullet, I will go with FMJ.
What counts when you need it is reliability, not "cute" or a "cool" shape, or a high price, or a gunzine writeup.
And speaking of price, if you carry, choose a reliable, but relatively inexpensive gun. No, not a $12 RG-10, but not an engraved, gold inlaid, diamond studded pistol, either. If you have to use that gun, there may/will come a point where police officers will order you to drop it. If you hesitate because your nice gun will be damaged, you won't have any further worries about the gun or anything else. Believe me.