When I bought my first Glock, I only planned to own one, and after some years of shooting different models, I decided the G26 suited my needs the best.
I was only going to carry it as an off-duty weapon, so a reasonable size was important. (I'd carried more than enough large and medium-size revolvers and pistols, so a smallish subcompact Glock appealed to me.)
The 9mm caliber was fine, and the G26 lacked the backstrap lump of the 19/17 (fit my hand better). I've long liked smaller revolvers and pistols for off-duty (and now retirement) carry, so the little G26 suited me fine.
I soon thereafter also bought a G27, but that was mostly because it was offered LNIB for an outstanding deal that was too good to pass up.
Shooting the G27 virtually as much as I've shot that first G26 (over 17K+ rounds each) has made me a better shooter G26 shooter.
I bought another G26 in 2010.
If I were going to do it all over, and only own ONE Glock for dedicated defensive purpose, it would be the G26.
Of course, when it comes down to shooting smallish 9's, I much prefer either of my S&W 3913's (standard and a late production 3913TSW), my even smaller CS9 (3") and even my SW999c (think P99 AS 9 compact). Better grips, triggers, heft and overall balance.
The little G26 is a gem among the Glock lineup, though.