I have a G17 and a G19. They are pretty much the same gun, the G19 being a little shorter in the barrel and grip. Both of mine are generation 3 Glocks.
I don't shoot my G19 much. It is one of my home defense weapons. It has never failed me.
My G17 is my target, plinking, and just plain fun 9mm. Shot a lot more than the G19, I have never had any problems with it. It really is a joy to shoot. For some reason, I like the G17 trigger over the G19. It seems better for some reason, and it does not have those "target trigger BATF import point reducing" grooves like on the G19. Not fond of those at all.
I suspect, since the G17 was the first Glock, and was designed around the 9mm cartridge, that it probably is the more reliable gun. The recoil springs are different in the G17 than the G19, stiffer in the G19 to compensate for the lighter slide of the G19. The recoil and action of the slide seems slicker on the G17. My guess is, because of these subtle differences, the G17 is overall the more reliable weapon with 9mm loads.
One more observation. The G17 seems to have little felt recoil. Like shooting a .22 almost - very mild. Follow up shots on the G17 are amazingly quick. The G19 is a bit more brisk in recoil.
All these opinions are subjective, but if I had to choose between the two, I would go with the G17.
Regarding hi-cap mags, of course, with either the G17 or G19 you will have to shop for 17 and 15 round pre-ban magazines. G17 hi-cap magazines are more available than the G19 15 rounders. Hopefully the AW ban will expire in the near future and this will be mox-nix.