Anthony Bez , Apr 16, 2007; 10:07 p.m.
Angela, You do not say what camera you use? The AIS Nikon is not well regarded for use with DSLR's. This means the lens is not expensive to purchase though. They sell for around $300.00 on the big auction site, which is less than the AF Sigma.
The Nikon 200mm AF is a different animal though, it is universally well regarded but comes with a hefty price tag, if you can afford one this should be your top choice. The Tamron 180mm AF has many admirers and I would advise as your second choice. The Sigma would be in third position in my pecking order.