The 24-70mm F2.8 L, is often the wedding work horse lens...but not necessarily on crop bodies. I find that to be an awkward focal length, it's just not wide enough on a crop body.
I've seen a lot of discussion about the 17-55mm IS by a lot of wedding photographers. The consensus seems to be that the image quality is outstanding, worthy of L...but that it does have other problems like dust getting in and the IS system crapping out. A few photographers that I know, have learned to only turn the IS on, when needed.
I also have the Tamron and find it to be pretty good...but I can tell that it's not an L lens.
If you want as good or better quality than the Sigma...your other options are the EF 16-35mm F2.8 L and the EF 17-40 F4 L. Perhaps the Sigma 18-50mm F2.8 but that's a lateral move.