I had the Canon 1.8 for a long time, and still have a 1.4. The 1.4 is better in pretty much every way, except for cost. But the 1.4 is just over $300 brand new at B&H right now, so it's hard to complain much about price. Sadly, the AF motor failed on my 1.4, and from what I read, that's fairly common with that model.
A lot of people dismiss the 1.4 because it's soft in the corners wide open. I think a lot of that comes from lack of field flatness. A not so great quality for copy work, but a really nice one for portraits on an APS-C camera.
At small apertures, the 18-55 2.8 zoom is actually sharper. But, it doesn't get to 1.4, and it only works on an APS-C body.
Don't laugh, but I think the new 40 f/2.8 pancake lens is a good alternative to all of them. 40mm turns out to be a nice, useful focal length for me. AF is slow, but very smooth and quiet. The lens is tiny, and in my tests, as sharp as the 1.4, maybe even better. Superior bokeh than the 1.4 I'd say. The corners are pretty dark wide open on my 6D, though software takes care of that. I paid $114 for my 40 brand new. But again, at 2.8, it's a lot slower than the 1.4.
If you care about sharpness wide open, with a big aperture, I imagine the Sigma is probably the best for the money. And if money is no object, just get the Zeiss and be done with it.