It really depends on the types of images you wish to obtain? The 70-200 f2.8 Nikon or Sigma are the standards if you wish to have a general telephoto capability. If it's for wildlife then you will need at least 400mm so the 200-500 would be better. Zoom lenses are more complex optically with more elements and so they will not have the same sharpness or contrast as primes but the recent (and expensive) long tele zooms by Nikon and Sigma are certainly approaching the best primes in terms of quality. If you shoot in the evenings then you need a faster lens ie: f4 or faster ideally.