I own a 19. I've messed with a 26.
Which to go with depends on what your concern is.
Actually shooting? The 19 every day of the week, and twice on Sundays. It is far easier to shoot, it is much more comfortable to shoot, it has a larger capacity, and it has a longer sight radius (greater practical accuracy).
Carrying concealed in a really difficult environment? The 26. It weighs less, has a smaller butt/grip. Width is the same.
I'd try a GOOD holster designed for IWB concealment for the 19 before I gave up on it. I second Adams Holsters. I carry a M&P40 FS with a TLR-3 off duty. That gun is bigger and heavier than a G19, and it has a flashlight on it. I can carry it comfortably under an untucked buttondown shirt or a polo with very minimal printing if I am wearing my Adams. If I am wearing my Raven Concealment Phantom, it prints readily, and is uncomfortable. The G19 is even easier to hide in either, but it vanishes in the Adams rig (just sitting it in there, it won't retain right).
The M&Pc is in between the G26 and the G19, and I own one that I do not use, because there are very few scenarios in which I can carry the M&Pc that I cannot carry the M&P FS, and in those situations I find I'm better served by something slimmer than either, like the Ruger LC9. I suspect that, with the right rig, you'd be in the same situation with a G19 and a G26. Are there situations where the 19 would not work but the 26 would? Probably, but not many.