Have to agree with the posters here who state the following:
1) Sig is a great platform. They are some of the most reliable, durable, well-constructed guns you can get. The decocker gives you very safe option for loaded carry without compromising use under duress. I have has a sig 226 in 9mm for 10 years and it remains my favorite self defense weapon.
2) Get the 9mm. There is little difference in stopping power, but greater control due to less recoil...plus 9mm is easier to find and cheaper. This is the caliber the p226 was designed for, and in my opinion is optimal for it.
3) Its a big gun for EDC. Personally I have no issue, but it is not compact by any stretch.
Would add that the short-pull trigger conversion is well worth it should you decide to go with the 226. Because the 226 is considered by so many to be one of the best handguns ever made, there are an endless supply of replacement parts and after-market options available, allowing you to customize easily to your preference. My $0.02.