Heres my opinion, I've had the Canon 35mm f/2, Canon 28mm f/1.8 and Sigma 30mm f/1.4, of the three the one i use is the Canon 28mm f/1.8
The 35mm f/2 is the cheapest, its pretty sharp, and doesnt flare easily or anything, However the Bokeh can get very weird, especially close to the MFD, it takes on a very "double visioned" quality that is VERY distracting to your image, if you work at a distance, it doesnt tend to crop up very frequently, but it ruined quite a lot of food shots i did, Still have it but am planning to sell it soon
The Sigma 30mm f/1.4 was really nice, Really well built, and the optics are jaw dropping on it, the bokeh is also amazing on it, However I didnt like the long MFD of the lens which I felt was very limiting for the stuff I use it for, I also got a bum copy that had unusable AF (But such a thing i could easily fix, I cant magically make the MFD shorter)
The Canon 28mm f/1.8 I found to be the best compromise, the sharpness is pretty good, the bokeh is pretty good, the AF is holy crap fast on it, and it focuses close so you can get up close to your subjects, it does tend to flare badly if you get the slightest bit of sunlight anywhere near the front of it, and the CA can be horrid on it, but these dont affect my shooting very often.... its also got a unique "look" to it i guess...
Here, have some 28mm f/1.8 samples

IMAGE LINK: http://www.flickr.com …unetsukiphoto/8055149744/
Impactful Pinkgenta
by
Kenjis9965
, on Flickr
IMAGE LINK: http://www.flickr.com …unetsukiphoto/8055149227/
Warm White
by
Kenjis9965
, on Flickr
IMAGE LINK: http://www.flickr.com …unetsukiphoto/8055149587/
Flower by the Road
by
Kenjis9965
, on Flickr
IMAGE LINK: http://www.flickr.com …unetsukiphoto/7333111368/
Tiramisu
by
Kenjis9965
, on Flickr
IMAGE LINK: http://www.flickr.com …unetsukiphoto/7333110660/
Glenlivet 18 Year
by
Kenjis9965
, on Flickr