Stila Diamond Lil is almost a dead ringer for MAC Smoke & Diamonds. I swatched them side by side, and couldn't really tell which one is which.
To be honest, I prefer Stila Diamond Lil a bit more than S&D because of the pigmentation and the buttery soft texture (although that means more fragile), and it also has a bit more sheen. But I don't think people can actually tell the difference when you put it on.