There are two basic possibilities if you need a stabilized lens in that range.
The Nikkor 80-400 4.5-5.6 VR (vibration reduction - first
generation)
The Sigma 80-400 4.5-5.6 OS (Optical stabilizer - an emulation of the VR
system)
It seems that Sigma did some reverse engineering because the optical performance and the stabilization are quite similar on both lenses. The differences are manifold but not related to optics.
Here is a short summary of my findings after testing both:
- build quality: slight advantage to the Nikkor but both are
excellent
- picture quality: identical (as explained in the tips page, you have to know
that you need to close down to f11 at 400mm to get the sharpest pictures)
- weight: the Sigma is the heaviest -> better stability, but of course
heavier to carry - matter of taste
- size: the Sigma is the biggest (extended to 400mm). On top of that, the
sunhood is huge -> very impressive and not too discrete (you get strange
looks while taking pics ;-)) - again a matter of taste
- stabilization: identical performance - you win between 2 and 3 stops (maximum
4 if you are very stable) - On the Sigma, choice between mode 1 (normal) and
mode 2 (panning); on the Nikkor, mode normal and mode active (when shooting from
a moving vehicle).
- price: advantage to the Sigma, but the delta is now limited (in Europe the
Nikkor used to be twice as expensive - now the delta is about 30%)
- tripod collar: perfect on the Sigma, I use it as a carrying handle - unusable
on the Nikon (even Bjorn Roslett is saying it is a joke... luckily, there are
good replacements like a Kirk one)
- AF: the speed on the Nikkor is depending on the speed of the body (D70 very
slow, D200 slow, D2X acceptable). The Sigma has a built-in motor, giving a
similar performance on all bodies. AF on the Sigma is much faster (close to or
better than some AF-S or HSM lenses), I would say on par with consumer level
AF-S lenses and a bit slower than pro-lenses (70-200VR for instance). The Nikkor
has a limiter button to speed up the AF process.
One drawback on the Sigma, the focus is a bit noisy.
- Noise: the Nikkor is relatively quiet, the Sigma AF and OS are a bit noisy....
My favorite: the Sigma
Some more information about the Sigma to be found here.