I have the 24-120 f4 VR and the 24-70 f2.8. They are both great lenses. If you are going to travel or use the lens as a "walk-around" lens, the 24-120 is great. But you really can't beat the 24-70 for portraits and events.
If you get the 24-120, you may find yourself really wanting to add a prime or two to your collection.