As I mentioned in an earlier post, the other option as opposed to the 24-120 is the 24-70 f/2.8. The advantage of the 24-70 would be that it offers a faster aperture, f/2.8 as opposed to f/4, meaning it lets more light in and it's better for taking pictures in low light. Generally, the 24-70 is the lens used by professionals that shoot weddings or other photo shoots, as it offers extremely good optical performance and because of its fast aperture. The only disadvantage of the 24-70 over the 24-120 is that it's 50mm shorter.
The 70-200 f/2.8 compliments the 24-70 perfectly, as the 24-70 stops at 70mm and the 70-200 begins at 70mm (where the 24-70 left off) and continues all the way to 200mm for telephoto shots where you need more reach. The 70-200 isn't really an alternative to the 24-70 or 24-120, while the 24-70 or 24-120 are just regular zoom lenses for everyday shots, the 70-200 is a telephoto lens used for getting closer to your subject.
The 24-70 and 70-200 are actually part of what's regarded as Nikon's "Holy Trinity" of lenses. The trinity consists of the 14-24mm f/2.8 (for wide angle shots), the 24-70mm f/2.8 (for everyday shots) and the 70-200mm f/2.8 (for telephoto shots). All three of these lenses compliment each other very well.
For more information regarding the 24-70 vs the 24-120, you could check out this
video on Youtube, which although compares Canon lenses, is still useful to watch.