I've had my 9mm Shield since the first week it was released, I now have close to 2,000 round through it, and still zero malfunctions.
I've had my Glock 43 approximately a year, and about 500 rounds through it, and zero malfunctions.
They are both very similar pistols, with the Glock being just slightly smaller. (My perception anyway.) It really comes down to what feels more comfortable to the shooter. These are both very fine defensive sub-compact pistols.
As far as accuracy issues go, I'm always a bit amazed how some people seem to believe that their concealed carry pistol should be a match-grade pistol, capable of sub MOA groups. The reality is these pistols were designed to be compact, reliable, and reasonably accurate. They were designed to be close quarters defensive pistols, NOT a sniper rifle. Yes, they should be held to a reasonable accuracy standard, which in the case of both of these pistols, they surpass the accuracy for a defensive pistol. The standard they were designed for is MOA, that's Minute Of Ambush.
I have always been concerned about putting a lighter match grade trigger in a defensive pistol. Under stress in a self defense situation, you are not going to be able to tell the difference between a 6-7 pound trigger, and 3-4 pound trigger. Your adrenaline will help with that. I'm also not very concerned with a crisp trigger reset, again because in a gunfight, I highly doubt the average person is going to be trying to only release the trigger just enough for the reset. I've interviewed several dozen people who have been in a gunfight, and the two incidents I was involved in, and trigger reset never was a consideration. Yes, for a match gun in say an IPSC combat match maybe, but the bullets aren't headed back at you from the target either.
Both of these pistols are excellent defensive carry pistols in stock form. It really depends on what feels the best to the individual shooter, as to which one they should carry.