I have been putting off for some time getting into DSLR, previously sticking with digiscoping or high zoom bridge cameras more recently. I had convinced myself that I would be steering toward the Sigma 150-600 Contemporary (probably with a Nikon D7200, which I don't yet own). Having read the many well-informed opinions and excellent pictures on this forum I have had to think again. Does anyone have any thoughts either way?
My opinion would be to go with a good copy of the Sigma 150-600mm Contemporary. Having tried them all, both Sigma 150-600s and the Nikon 200-500 are superb lenses, although I suspect there is a fair bit of sample variation among all of them, which may explain why there isn't a lot of consistency across the various online reviews.
I rented both the Sigma Contemporary and the Nikon 200-500, and compared them side-by-side a couple of months ago; the Nikon was a little better in the corners (especially full-frame corners), and had a more stable in-viewfinder VR image, but the Sigma was equally sharp in the center, lighter, cheaper, had more reach, and was customizable using the USB dock. I wound up buying a new Sigma Contemporary, and was pleasantly surprised to find that the one I bought had sharper corners than the one I rented.
Later, I rented a Sigma 150-600 Sport and compared it to my Contemporary, and found image quality and AF speed virtually indistinguishable. The Sport is a lot heavier, and has a more robust build, but the Contemporary also feels very well-made. Both have very effective image stabilization, and I'm able to get consistently sharp shots down to 1/160s at 600mm handheld.
So I'm pretty satisfied with the Sigma 150-600 Contemporary as my long lens of choice, but they are all very good telephoto lenses, and definitely better than the telephoto zooms that came before them (e.g., the Sigma 50-500 OS).
Here are some comparison images I shot with the Sigma 150-600 C and the Nikon 200-500 when I rented them; as the filenames reflect, these were on both a D810 and a D5500 (which has a very similar sensor to the D7200), and also compared to my other telephoto lenses, the 500mm f/4D AF-S II and the 300mm f/4E PF VR:
https://drive.google.com/open?id=0B4M7Ie_2T_HgZ0tBcjg3eUozd0E