I say #2 is the sigma. Difference in the corners and the edges. More detail in the fence on the left edge, as well as the rain gutter on the house (upper left). Right side not much difference.
The 2nd image (which is apparently the Canon) has more detail to it. Yes, even at f/8 it can be seen.
And to those who say "I didn't buy an f/2.8 lens to shoot at f/8" I say you're foolish. Different scenes benefit from different techniques. f/8 Is just as useful as f/2.8. They do different things.
The reason to have an f/2.8 zoom lens is so that you can do more with it, not so you can always shoot everything at f/2.8.