The 24-70 II is just as sharp at 2.8. At 2.8 the 24LII has less vignetting by the time is is stopped down to 2.8 and less distortion all the time. The 24LII lets in 4x the light when you need it and that is really the main feature to make a descision on.
Yeah, agree with that...they're a bit hard to compare. I have a 24-70 II and sold my 24L to fund it. It's a great, great lens but I tend to use 24mm lenses stopped down (for low light shots I take the 35L).
Did some testing and I can confirm what saneproduction said; at 2.8 they are about as sharp but the zoom has some vignetting and distortion, although both can be quite easily fixed in post.
However, if you look at mid-contrast, colors, etc. I really think the 24-70 II is a prime killer, I use it most of the time now.
What saneprod said. I still own both, and also the TS-E 24mm mkII. I did a quick and dirty test of my kitchen tiles. Exifs are intact, look at "max lens aperture" to see which is which:
I have a hard time to justify keeping the 24L now - the new zoom is unbelievably sharp wide open. If you do a lot of video, or low light stuff, though, you might want to keep the 24L, as distortion and vignetting might be an issue in some scenarios.
