I had both, loved both. SIG is my favorite semi-auto in 9mm, hands down. I have had several actually.
The 226 actually has a somewhat nicer, more sculpted E2 grip than the 229. It is wonderful in the hand. Obviously, a slightly longer barrel may shoot better for you.
That said, I found I shot both just about equally. I ended up selling the 226. My reasons:
1. The 229 can share magazines with my 228 (which I would say is the best SIG ever made...the balance is perfect).
2. Mounting a weapon's light (for night stand duty, a primary mission for this particular gun), I found that the balance was better with the 229. The 226 felt just a little more clunky.
I do wish I still had the 226. Would love to have both, but could only have one for budget purposes.
If this is not fo CCW and you will do a lot of range shooting, AND, not planning on putting a weapon's light on, then go for the 226.
If you want a gun for a defensive role, with a weapon's light, rather than a range queen, than the 229.
The 13 v 15 round magazine argument is null. There are plenty of 15 round mags for the 229. I personally like MecGar's.
Hope this helps.
[if you can...get both...maybe one Elite and the other a standard E2....you CAN use 226 mags in the 229...so if you do have a need for two side arms, get an Elite SIG and a standard. One 226, one 229]