I only carry spare 17 mags for my 19 and 26. They are much easier to grab out of a pouch and get a solid grip on without fumbling the reload.
Wow, 5 pages of this discussion? It's not like the 17 mags cost $10 more than the 19 mags. just try one and see how you like it.
Regarding adding extensions to 19 mags as opposed to buying stock 17s is there any concern for the durability (from being banged around, dropped on the ground during reloads, etc) of the 19 mag + the plus 2 extension vs the stock 17 mag?
I personally have not had problems with G17, G23, or G22 mags w/ factory +2s on them in this regard.
Been running some of these for years, they've been banged around, dropped in rocks and concrete, been put through hard use in general, like other mags I have.
Never a problem, so I would not hesitate to put some on G19 mags and expect the same.