TS-E 24mm f/3.5 L II

[Trowski]

Those lenses are so different that really the only thing they have in common is focal length. I think the question you have to answer is what is your primary use for the lens going to be? If it's for landscape, then I highly recommend the TS-E 24mm. You really won't get better image quality in that focal length range (the Zeiss 21mm previously mentioned is close though and there is also the TS-E 17mm, but 17mm is quite a bit wider). There's just nothing that can match the creative abilities you get with a tilt-shift lens. It will do things that you can't do with your other lenses. If landscapes were only a minor interest, then the 24mm f/1.4 is great for just about anything else.