I moved from Canon to Nikon having used the Canon 24-70mm f/2.8 and Canon 24-105mm. Was never truly happy with either, the 24-70mm went back to Canon for adjustment, came back decent sharp at 70mm, but 24mm was not as good. For landscapes the 24mm end suffered in the corners.
The 24-105mm was a sharper lens, but suffered from horrible barrel distortion at the 24mm end.
The Nikon is brilliant, sharp from 24 to 70mm and at f/2.8, it is also a bit lighter than the Canon 24-70mm f/2.8.
I started wedding photography last year and this was one of the reasons for moving to Nikon, it sits on my D3 with a SB-900 as the main workhorse for wedding work and I have complete faith in it and that set up.
For landscape work the 14-24mm is sharper, but then that is an outstanding piece of optics, but it is only a 2x zoom while the 24-70mm is a 3x zoom, also the 24-70mm can take filters which is why is sees more use than the 14-24mm for landscape work.