I've found the biggest factors for me for concealment are (1) grip length, (2) width and (3) weight, probably in that order. And for me, it also depends on what I'm wearing and what I'll be doing as to whether not something is going to be "best" for concealed carry.
The two 9 mm's I carry are either the Walther PPS, very slim, short grip, carrying 7+1, or a G19. I have an easier time comfortably conceal carrying the Walther PPS in dress clothes. If I'm in jeans with a heavy gun belt, I go with the G19 as a 9mm carry gun. There's a significant difference in size, weight and capacity between these two guns. There's times when I will trade off capacity for size.
However, if I had to choose between the G26 and G19, I'd probably go with the G19. I don't own a G26, but I've checked them out, and I don't believe I gain much in concealability over the G19.
I agree with you, width is important for a concealed carry gun and the G26 and G19 have the same dimensions in that matter.