I own both a full size S&W and a SIG GSR. While both have been flawless performers, I'd give the edge to the Smith.
As to the SIG, one really needs to understand the history of the gun. There have been three basic production periods: early custom; early custom/in-house; and what i would call in-house regular production. It started out much as a custom 1911 with much of it being assembled from parts from top 1911 parts suppliers. Early guns, something like the first 100 to 150, were finicky as they were very tight and required much hand fitting. As time went on SIG made more and more of the parts in-house and while the guns were less and less custom in nature the problems were ironed out. If you do a search here or at the 1911 forum you will find a discussion of the serial number range to buy above if you are looking at a used gun. My gun is an earlier one (with the sewer cap on the right side of the slide) but was produced from a time when there was still much custom about it but problems had been ironed out. As I said, it has been flawless. The problem is that much of the early issues that plagued the gun, ones since resolved, have followed affecting the the gun's reputation. That's not to say that there aren't occasonally issues with guns being produced today, but fortunately early issues have been left long behind. As with any gun that has teething problems the gun still carries the faint aroma of that discontent.
As to holster issues, yeah, the P Series slide profile can cause fit issues. The slide is no thicker than other 1911's (and a bit thinner than some) but the profile that makes it unique can cause problems with fit.
That said, I'd still give the S&W the edge.