[VinnyP]

If you were only going for one lens then I'd go for 1 or 4. 4 gives you more reach but I haven't used it. I did own one and it was a very flexible lens but out of those 2 I'd go for the Sigma. With any lens that covers that kind of range you have to compromise a little on performance and image quality. The 70-300 and 55-200 would not be great as an only lens. But for the same money as the 18-200 you can get a Tamron 17-50 and teh Nikon 55-200 or 70-300 if you think you could handle changing lenses these would give you a lot more possibilities.