I believe the SIG will be a bit more accurate gun, just because the trigger is usually better than any of the Berettas I have handled. That's the big deal, as far as I am concerned.
I hear lots of complaints about the feel of the Beretta as far as fitting the hand goes. And the pistol is just plain BIG. 226s are not small, but the 92-series guns are just too big overall.
Some will caution you to be careful to avoid of the so-called "mud rail" guns when buying an older P226. I have had two, and still have one. No problems, so far. I am not sure where the mud rail frames fell in the P226 serial numbers, but you can easily identify them just by removing the slide and looking for the mud relief areas in the frame rails, if that is something that is a concern to you.
I would buy the 226.