It's all according to what type of photography you take ?
Landscapes usually require wide angle lenses (circa 20mm) , portrait type shots work well around 50mm, Sports / wildlife photography may need a telephoto circa 200/300mm plus. Then chuck in to the equation do you want the convinience of a zoom lens that covers a range of focal lengths, or seperate more dedicated lenses for optimum image quality ?
The 18-70mm lens is great way to start & covers a general range. Some people prefer to have a lens that does it all & go for the Nikon 18-200mm lens. Hey if you go for a non Nikon lens, you can get 18-250mm now
