Nikon 200-500mm, Tamron 150-600mm, Sigma 150-600mm C, Sigma 150-600mm S.
Depending on who you speak to, what you read etc etc there are varying thoughts on which lens is best between the Nikon, Tamron and Sigma C. From reading around I've found that that general consensus is that the Tamron is arguably the sharpest in the centre at the tele end, but suffers more in the edges (less important in super teles), but a close call with the Sigma. The Nikon is the best at shorter focal lengths.
With there not being any real discernable difference between the Nikon, Tamron and Sigma C it begs the question why you would pay £1150 for the Nikon when the Tamron and Sigma are £739, especially as the Nikon weighs 2.3kg vs 1.9kg for the Tamron and Sigma. I have the Tamron and it's great, although if I was buying now I would buy the Sigma C so that I could use the dock with it (Tamron was £200 cheaper than the sigma when I go mine). I find the Tamron 150-600mm on my D750 perfectly useable hand held.
Then there's the Sigma S, built like a tank and optically the best, but costs £1200 and weighs 2.9kg. It would be up to the individual as to whether these sacrifices are worth the 5% improvement in IQ.
All have IS (VR, VC, OS) but as mentioned above, at fast shutter speeds IS isn't needed and in fact some people say it can be a hindrance.