I've never tried out any of the Sigma lenses, but as with most manufacturers, the reviews differ for each lens. I'd recommend following up with any photo forums/websites out there (and please let us know!).
I have a Nikkor 60mm, the stock lens, and a 70-300... like them all, although the zoom lens is rather cheap.
I have a Nikon D50, and a 70-210mm Nikor that give great results. The 70-210 is about 10 years old. I don't know how much Nikkor lenses have changed. The 10 year old AF lenses work perfect in my new D50. Hats off to Nikon for supporting their existing hardware! My Brother In Law has a set of Sigma lenses for his Nikon film camera and has some great art to show from them. You get what you pay for though...
Hi jjmm
Sigma makes some nice lenses, but the 70-300 isn't one of them. It's very soft, especially when you compare it to a comparable Nikon glass. I'd invest my money elsewhere. Nikon/Nikkor is a safe bet for high quality glass, and they hold their value very well. Also, if you don't need the focal range, get something with less zoom.
I hope you aren't planning to shoot aquarium photogs with a 300mm telephoto
To All,
Many and sincere thanks for the thoughtful notes. Based on your inputs, I have decided to suck it up and put a few extra $$ out to stay inside the envelope with Nikon lenses.
Best regards,
jjmm
You won't regret it, both from image perspective and from a financial one... if you ever change to another body style, you can resell the nikkor's for a great deal more than others due to high quality.