I have the Sigma in that range and am very happy with it. I would recommend comparing it with the Tamron. (My only experience with Tamron is a telephoto lens I used in Antarctica, under cold conditions. I was not pleased with it at all.) I bought the Sigma for the same reason you described looking at the Tamron--the Nikon was much more expensive.
Currently my primary cameras are a Fuji X-T2 and a Fuji X100F.