I have both and have carried both. I like both very much. I now carry the Sig primarily. The reason for me was that with my grip I ride the slide of the Glock a little too hard and have had a strange failure where the spent round is ejected, but the slide didn't travel back far enough to chamber a fresh round. This resulted in a click instead of a bang, hence the change.
The Glock is slightly smaller and definitely lighter. It also holds one more round in the magazine. The Glock points better for me with its lower bore axis.
The Glock also has more felt recoil and with high volume shooting in hot and humid conditions the checkering on the back of the grip started to irritate my hand.
The Sig has less felt recoil. Due to the frame size I don't ride the slide with my thumbs, so no click when I expected bang. With the proper belt and holster I don't notice the size or weight difference from the glock. One round less does not cause me distress. It has repeat strike capability and the trigger is very nice.
You really can't go wrong with either gun. They are both reliable weapons and can be easily carried and concealed. I would go and hold them both and see which one feels better. Of course price might be a factor as well. You can probably find a Glock for about $500 where the SAS will run you $800 - $900.
Good luck with whatever you choose. You won't be disappointed with either.