Thanks Schmoelzel 
If you don't mind not having the speed and silence of USM autofocus, the 28/2.8 would be fine.
I've heard the Sigma 28/1.8 is fine optically, but the autofocus is supposed to be quite bad.
About a month ago, I too wanted a normal focal length for my 20D, and was torn between the 28/1.8, 28/2.8, and 35/2. In the end, I opted for build quality and bought the Canon 28/1.8 USM.
This lens is beautifully built. It's exactly like a slightly smaller 85/1.8. The autofocus is fast and SILENT! It also has full-time manual focus (which the other 2 lenses dont). Another bonus with the 28/1.8 is that it has 7 aperture blades, vs only 5 for the 28/2.8 and 35/2. I can say that the bokeh on the 28/1.8 is fantastic, as is the colour (slightly warm) and constrast.The lens is useable from f1.8 to f2.2... although not tack sharp, the shallow dof really hides any lack of sharpness. By f2.5, there is a noticable jump in sharpness, and from f2.8 up it is very good.
I initlally thought the lens was producing soft pictures, however I later learned that using a normal lens will produce much different looking pictures than a lens that leans towards telephoto. This is probably why some people complain that their 17-40L doesn't look like an L lens should. So, to put my mind at ease I did ALOT of testing with the 28/1.8 and the 50/1.8II. I tried to match focal lengths as much as possible. What I found is the these lense are very close in sharpness, but because of the different perspectives (distance compression), it's very hard to compare. In some cases I found the 28/1.8 to be sharper, and in others the 50/1.8 was sharper. But it was really close either way. I am now a very happy camper with this lens and I can recommend it whole heartedly!
One more surprise, this lens has a VERY good close focus distance!
Here are some sample pictures....
- 28/1.8 test pictures
- 28/1.8 real-world pictures
- animated gif compression comparison 28 vs 50
- 50% crop at f7.1
- large picture taken at f2.8
- 100% crop showing closeup abilities
Please feel free to ask me any questions you want about the lens.
EOS R6 Mark II - Sigma 50/1.4 Art - Sigma 14-24/2.8 Art - Canon EF 70-200/2.8L Mark III - Godox Xpro-C - Godox TT685C x2