I own a 226 in 9mm and an XD 9, though it is the sub compact and thus a different animal with that shorter barrel. I also used to own a SigPro in .40 and have shot a 228 (9mm), 229 DAK (.40), and 4" service XD in 9mm.
For sure, I am no expert, but I do know that all these are fine weapons. I like shooting both. They are all reliable, feed, shoot, and eject everything I put in them. But, the Sigs andd XDs FEEL so different from each other because ARE different from each other. Of course you should shoot both types before buying, but if you can't and you must make the decision, then go with your wallet and your gut. If price isn't the issue and your lust leans to the Sig, get it. If the cost of the Sig is too steep, then get a used one or go for the XD. The XD might not have the "image" of a Sig, but the XD will serve you well.
As for me, I'm in the market for another 9mm and having the same dilemma. I love both my 226 and XD SC, so it's either a new 228/229 or a 4" (Service model) XD. Frankly, if the funds get rounded up, it's going to be the Sig and most probably a 229 DAK. But, if the money is too much of a stretch, then I'll have no regrets going for another XD. In short, I'm saying that in Frandy's universe, it's strictly a matter of how much to spend. I trust either firearm.
FWIW