I've owned or do own all of the models in this thread. None of them are bad choices. I stick with the 26 because I am by now very comfortable with tucking my little finger under the grip, and shoot it even better than my 19X, 19, 17 or 34. But it takes getting used to. But they definitely will do the job. Just needs extra training.
The 43X is really a great choice. Grip is smaller than the 19. Very accurate. Decent spares, plenty of accessories and holsters. And it carries well. Plus Shield mags will get you 15rnds without any extension.
Don't license Sec 15 before Sec 13. License it for the main purpose you are buying it for. If that's SD, then license it as such. In spite of what the GS and GOSA fanbois will tell you, the truth is that SAPS IS eventually going to amend the FCA, and they WILL close that loophole of carrying sec 16 or 15. They aren't dumb, and they know they slipped up when writing the act. Just make your life easier and do Sec 13 first.
Another great choice (if you can find one) is the HS11 "Hellcat" which is as good or better than the 43X. Sig P365 is very good too, but overpriced and lacks backup service.
That said, if someone wanted to only ever own ONE gun in their life, it should be a G19. Lots of reasons.
HK...don't bother. CZ P07 or P10? Not bad choice. They are decent.
If you want something to SD and also play on the range a decent amount of time, get the 19. Doesn't matter which gen. They all work 100%. If only for SD, get something a bit smaller. This is SA. Shorts and a T-Shirt don't hide big guns easily.
Ask if you have any other questions.