The sigma 30 1.4 is a better buy than the canon 28 1.8 for crop IMO.
The siggy is sharper, has smoother bokeh, and is 1.4 vs 1.8.
The canon however, can focus a bit closer, and has slightly faster AF.
A better buy because of the 1.4, but I think in real world use, the sharpness and bokeh isn't significantly different. If the Sigma had reliable AF, I would still have it in my lineup. However, with all 3 copies I owned, I never felt confident that it was going to hit focus. I'd say it would nail the shot 60-70% of the time. That may be perfectly fine for most people, but it annoyed the hell out of me. The 28mm has been more like 90% accurate, even in low light...that's something I can live with.

