I've carried both and for a CCW and if you will be constantly carrying, I prefer the G27. With the Pearce +1 Exetension you can get 10 rounds in the chamber or stick with the 9 rounder for deeper concealment. The Glock is also more corrosion resistant. If the day comes when you have to put your pistol away still wet and dirty, and you have to run to work and won't be able to clean it until the next day- you don't have to worry with a Glock. The Glock 26/27 models can also use the magazines from their full size counterparts for more capacity.
Both pistols will accept barrels for .357 Sig making them versatile.
The Sig is a better choice if you can afford to carry a slightly larger weapon. This in part is based on how you dress. I personally want the smallest most effective weapon I can conceal comfortably. The Sig is also more comfortable during practice sessions due to the longer grip. The Glock trigger is nothing to brag about, but nothing can compare to the smoothness of a Sig double action and the crisp let off for single action. Sigs are great in that aspect. And something about hearing the slide rack back and forth and listening to it..makes ya just grin!
But to answer the original question, the Glock is definitely more concealable.
Good Shooting
RED