I could have bought a full frame camera...
Yes and also pay twice as much for lenses. Fullframe is, including lenses, at least twice as expensive as prosumer crop. So that's no comparison
For the price of a FF body with good all-round lens you can buy an excellent prosumer crop with a good prime, good allround lens, wide-angle and good zoomlens.
I have considered both the Canon and the Sigma and decided that the Canon just wasn't worth it for me, it's a bit sharper towards the corners in wide aperture, but the Sigma was better with something else, I believe resolution. So they were more or less the same in terms of image quality but the Canon was more expensive, Sigma offers better warranty ánd you get a lens hood.