I have the Nikon 200-500mm (since 2015 - and back then the lens was really revolutionary) and am VERY satisfied with the image quality and the VR is also excellent (a gem for this price).
The autofocus is rather slow. But once the object is in focus, the speed is also sufficient for tracking and the focus ring is easy to use/well placed.
Negative: the zoom ring takes a long time to move from 200 to 500mm (sometimes I have to readjust)

I have also been using the lens on the Z 6 since 2020 (with the FTZ adapter): the autofocus works very well (which is not the case with all F lenses). Use it for photo and video (VR is great).

The Nikon is probably heavier than the Tamron, but the in-camera corrections work properly with Nikon-to-Nikon. But I don't know the Tamron. (I think only owners of the Nikon will answer your question here)

I have never regretted the purchase, but today I would pay the 500.- extra for the Z 180-600.

Hello
I have had the Sigma Sports 150-600 and it was very good, but the 180-600 in a Z is MUCH BETTER
I now have the 180-600, is the best choice you can have, no doubts.
I have shot surfers with a Z6 II, and last summer with the 180-600
Super lens.

I have owned the Nikon 200-500mm for a long time and am very satisfied. The price is good for the quality. VR is also very good. However, for my needs (birds in flight) the autofocus is not fast enough, but for everything else sports/action it is absolutely sufficient. I will soon buy the new Nikon Z lens 180-600mm and sell my 200-500mm. If you are interested, you can contact me (mau.riz.io@hotmail.com)

I've had the AF-S Nikkor 200-500mm for several years and am happy with it. I bought it for my D810 back then and now use it with the adapter. It works well. But to be honest, if I "had" to buy it again now, I would buy a lens directly for the Z. However, I don't know the Z variant :-) Why don't you hire both lenses first and then decide?