To be clear, I was referring to landscape details; I've definitely encountered situations where a narrower field of view than a 55mm lens can provide would be most useful. For plants, true macros are somewhat out of my price range, but I have seen some good examples (as in coldrain's link to pbase.com) that suggest that the 70-300 is reasonably suited to botanical work.
Looking at those MTFs, it strikes me that the dropoffs on the 70-300 G should be mitigated somewhat by the digital sensor size. Always hard to tell about such things, though.
Definitely going to have to think on this one a bit more before I buy anything, though. Thanks for all the advice...the 55-200 is definitely a lot more in consideration now than it was when I first started.
You are partly right in that the MTF charts for the 70-300G are for full frame, and that you will avoid the extreme fall-off of the edges.
But that does not make things all that rosy for that lens though. If you consider the APS-C size, you still come up with very low figures.
Sharpness for the 70-300G at 300mm, 0.64-0.5. If 1.0 is the resolution your camera can resolve... this lens limits that by almost a half.
In contast to the 55-200 Nikkor: its sharpness hovers around 0.8 with a dip to 0.69. That is not a subtle difference.
The Sigma 70-300 APO DG, according to the MTF chart: 0.83-0.77.
Contrast:
Nikkor 70-300 G: 0.83
Nikkor 55-200 DX: 0.95
Sigma 70-300 APO DG: 0.95-0.93
I know whichone I would avoid.
About your purpose for the lens: Even though the Sigma has just one year warranty, with its 1:2 macro ability (and its much better sharpness and contrast) it does seem to be the best option in this price range.
Now that I understand what you want to shoot with it ( I would not call that landscape photography) I do understand your choice of lens type. I myself make a LOT of photos like that, mostly with my Canon EF 70-200 f4 L, with or without 1.7x tele convertor.
Those two cost quite a lot more together than your intended budget of course. And at times, I bump into its limitations still, and wish I had a tele macro lens (I have a tamron 90mm f2.8 macro), like a Canon or Tamron 180mm f3.5 macro (a Nikon 200mmm macro will not AF on my Canon, unfortunately).
A short macro lens is not always the right tool, because you have to come close to the subject to make a photo. A very good macro lens does not have to be very expensive though. The Sigma 50mm f2.8 DG is as sharp as anything, good colour and contrast too, and under $250. A steal for such a lens.
So in view of your intended use and your budget, I still feel the Sigma will make you happiest. Otherwise, go for the 55-200 nikkor, and get a set of extension tubes to experiment with macro photography.