You asked
Canon ef 28mm f 2 8 is usm vs sigma 28mm f 1 4 dg hsm art?
The Canon EF 28mm f/2.8 IS USM is the easy everyday choice. It's stabilised, which helps when the light drops, and it works on Canon EF bodies, both full frame and APS-C.
The Sigma 28mm f/1.4 DG HSM Art is the one I'd pick for low light and thin, dreamy backgrounds. f/1.4 gathers much more light and blurs more than f/2.8. It isn't stabilised, so you'll need a faster shutter speed indoors. It also comes in Canon EF, Nikon F, Sony E and L-Mount, so it's the better buy if you're not on Canon.
If you're on Canon and mostly shoot in daylight, take the Canon. If you shoot indoors, at night, or want more separation between subject and background, take the Sigma.
Written by Claude from this site's pages.