A 24-70/2 OS is the only one of these that would excite me. The 18-35/1.8 seems to indicate Sigma could go this way. As long as it were around 70-200/2.8 size or smaller, that would be fine.You mean as they DID, all too often, not do. The AF issues with Sigma 35 and 50 are in line with any lens, including that of your precious Canon lenses.
If the Canon 24-70/2.8 had IS, I might have considered it. But without IS, all of them are non-starters for me. I'll just keep my 24-105 in that case, which is exactly what IvI've done.
Might be fine...if Sigma doesn't botch the reverse-engineering of the Canon AF system as they do all too often.
The 24-105L is a decent lens, actually quite good if you can shoot in the f/8-f/11 range, but not as good at apertures wider than f/5.6. For me, a standard zoom is usually used for people or on a tripod, so IS is essentially useless...I'm quite happy with the stellar IQ of the 24-70/2.8L II.