AJ said:
Both Canons have too much magenta in the skin color. The Sigma has better yellows in the background.
In addition to what the others have said, don't forget that your screen's colour is unlikely to match the colour of the screen the files were edited on, and as such your screen may be showing a stronger or weaker representation of one band than another, causing there to appear to be more of a difference in colour between two images which could look closer together on another screen.
Which isn't to say there won't be a difference in colour rendering, because there almost certainly will be between any two given lenses, just that you can never rely entirely on viewing results somebody else has come up with in this fashion.
For what it's worth, I'm looking at this on a 100% sRGB screen here (given these are .jpgs on a regular common website, there's no chance they exceed that colour space) which I recalibrated just two days ago (so not much chance of any colour drift yet) and the difference I see between them in colour is virtually nothing. Certainly nothing which couldn't be equalised with the most minor of white balance shifts (I'm talking +/-50k and +/-5 on tint, here).
A slightly bigger issue is in the main run of 'comparisons', the framing is slightly different. Either these lenses are all showing very random focus breathing (not likely) or they moved a little closer on some frames than others (extremely likely). That does influence apparent resolution, as well as the look of the background, of course.
Anyway, I really don't think it's surprising that the answer is they're all really good and in 9/10 situations you won't be able to tell the difference between them, so buy whichever one is most easily justified within your budget. Nobody should be surprised the old favourite 85mm f/1.2L is good, nobody should be surprised the instant-classic Sigma is good, and nobody should be surprised that a brand new L prime is good.