ageha -- I haven't used those lenses personally, but judging from Bryan's reviews over at The Digital Picture, neither of the lenses are great performers. he certainly doesn't seem satisfied with the image quality from the 28 f/1.8, and the 35 f/2 can only be described as decent for its price range.
also unfortunately, none of the sigma primes in this range are very strong performers, so the fact that they exist doesn't help the selection process much for those in need of a cheap fast wide-angle prime.
I know there's a lot of people on the forum, myself included, that would love to see Canon refresh its lineup of non-L EF wide primes