G19, one of my favorite pistols. My other favorite is the g23, which I have set up with a .357 barrel right now, just for kicks.
Upgrades I've made to both are Wolff springs with steel guide rod. Couple thousand rounds down the G19, and no problems whatsoever. I put an extra power recoil spring in mine, just by one pound, and it shoots soft. I upgraded the trigger with a Haley Skimmer trigger just a few months ago, and even after all the rounds on the trigger that was in it, the Skimmer was a noticeable improvement. Not necessarily smoother, but it doesn't have the hitch in its giddyup anymore. For sights, I initially put Trijicons on it. But after 15 years or so, they were pretty much shot. My next sight set was the Ameriglo I-Dot Pro. HUGE improvement in my accuracy. It uses a dot-over-dot sighting arrangement, with a front tritium vial augmented by a big green phosphorescent ring around it, that really draws your eyes to the front sight, especially in transitions from bright light to dim, such as entering a shoot-house. The ring glows bright for about 5 or 10 minutes, long enough for your eyes to adjust to dimmer light, if need be. The rear dot has no outline, so the rear sight is black unless you're in the dark, in which you put the dots in the 8 configuration, and go to town. It has made shooting my G19 almost as easy as shooting a red-dot, IMO. Highly recommend it. Incidentally, the Ameriglo's have Trijicon trademark on the side, so I'm pretty confident in their reliability. I liked them so much on my G19 that I upgraded my G23 very shortly thereafter, even though the Trij's on it still had plenty of life left. If you're not married to the three-dot sights (which I really wasn't), the I-dot's have a lot going for them. And really, since a defensive encounter most of the time will be against a predator that primarily is oriented vertically, you can accept more error in the vertical than the horizontal. So, putting the dot over the dot, and then the front sight ON the target (for me, the I-dots need the front sight centered on the target for the POI to hit the intended POI), you should get good hits.
For me, the I-dot Pro's were the best upgrade I've done to any pistol, for my shooting. Triggers, extended slide releases, extended mag releases, all these I've done, and all are incremental improvements, but really just for feel (except maybe the trigger). The sights, though, immediately helped me shoot better. Most of my experience shooting is in IDPA, incidentally. So I'm not talking about just standing behind a bench and doing bullseye shooting.
