I prefer the 19/43 combo. I like my larger guns to still be easily carriable, thus 19 over 17. Then, since the larger gun is carriable, there is no need for the middle ground (the 26, in this case), so your smaller gun may as well be really small, hence the preference for the 43.
Before anyone jumps all over me, I know the 17 and others in its size class are carriable if you have the right belt, right holster, hold your tongue just so, and the moon is in the seventh house, but it is larger and heavier, and all you are getting out of the deal is 2 more rounds, which doesn't seem worth it to me.
With all of that being said, unless purchases are already made, think about looking outside of Glock, as well, especially for the single stack. There are many good options, and a lot of them will give you an extra round or even two over the G43 without sacrificing ease of carry. Of course, if you just prefer the Glock, more power to you.