Hi Charles,
For your info, all my flowers or macro shots (if you have already seen them) were shot with the mentioned Sigma 105mm lens. Despites a Sigma and not a Nikon macro lens, what it can produce have never failed to amaze me.
Technically, most lenses out there are better or over-rated than most users around, including myself. So, I would be contented to own any of these macro lenses:
1) Tamron 90mm
2) Sigma 105mm
3) Nikon 105mm
Reviews/rating I had read for the above 3 lenses three years ago and also recently this year was ranked the same as above.