I have both, and these days, I prefer the 226 over the 229, mainly because the extra half inch of barrel length gives me about 100fps more out of the 357SIG round over the 229.
For all intents and purposes, they are really the same size gun. The 229 is a little fatter in the slide, the 226 is a little skinnier and a half inch longer, neither of which means anything carry wise. Personally, I find the 226 has a slightly more comfortable grip, even though its virtually the same size as the 229's.
If your looking to choose, your best bet is to go to a shop that has both and compare them side by side. While very similar, they both have their own feel, and you may like one over the other for whatever reason. Better yet, if you can rent them and shoot them, you'll have even a better idea. I doubt you'll see any difference there though either. Mine all seem to shoot the same.