Sigma 30mm f/1.4 or Canon 28mm f/1.8 or others?

I've read a few threads mentioning how great the Sigma 30mm is, but I don't think they were specific about comparing it with other options... so I'm hoping for those who have any similar lenses to give some comments on them thanks!

I'm using a 500D and currently have the 15-85mm lense. I'm considering getting a lense for better low light performance and have come to the conclusion that around 28-30mm would be a good focal length, though possibly stretching the acceptable range to 24 and 35mm if the lenses should be considered. (the Canon 35mm f/2 is quite a bit cheaper but Im a bit worried about the length and the aperture specs)

At the moment I'm mainly looking at the Sigma 30mm f/1.4 and Canon 28mm f/1.8. I've looked at another website which suggests the Sigma is softer than the Canon and looking at the distortion chart it appears the distortion circle has a lot of 'squiggles' and am not sure what this means?

In terms of price, the Canon is 20% more expensive than the Sigma. To me, the Sigma has the advantage of a large aperture (which is the reason why I'm considering such a lense) but have only ever used my current canon lense so not sure about Sigma as a brand (i know it's very reputable), it's quality etc.

I guess for these lenses there is no consideration of image stabilisation? would this be correct?

Any comments much appreciated!