If you can live with f2.8 then the Canon 28mm (non IS) is an exceptional little lens for the money, same caveats as the 35mm-
Old school AFD focus
5 aperture blades (poor bokeh compared to more expensive lenses)
On the plus side, very cheap, very compact, nice and sharp, fast to focus, nice angle of view on APS-C.
If you want a 24mm then would you consider an MF lens such as the Samyang f1.4....
If you can live without AF and cope with a manual iris that closes before exposure when stopped down (that is conventional EF lenses only stop down at the point of exposure, they keep the viewfinder nice and bright to assist composition and focus) then it is a superlative lens for the money.
I haven't heard brilliant things about the sigma 30, I was on the cusp of buying one but could find no decent reviews.. all middle rated.