Both of the above replies contain good advice, IMO.
It's difficult for me to conceal a G19 with what I normally wear in really hot Summer weather. The short-gripped G26 is much easier to work with under these conditions. During the rest of the year, however, the G19 is probably a better choice. As kg333 implied, you can make a small gun bigger and easier to handle by adding a grip adapter to a longer magazine (or just using a longer mag by itself), but you usually can't make a big gun smaller unless a hacksaw is involved. I'd usually agree with the basic idea expressed by kg333s comment on subcompact autoloaders, but the G26-size Glocks shoot as well as many full-size service weapons if the shooter just pays attention to the fundamentals of shooting, so at least where Glocks are concerned, the smaller guns aren't too much of a handicap.
I'd probably recommend getting the G26 only if you MUST have one gun for everything, including concealed-carry in every season. Otherwise, you'll be better off getting a G19 now, and perhaps adding a smaller weapon for concealed carry during the hottest months. A G26 is the one of the smallest Glocks, but that doesn't mean it's truly small when compared to all other pistols.
"Placement is power" -- seen in an article by Stephen A. Camp
(RIP, Mr. Camp; you will be remembered, and missed)