Tamron VC or Nikon VR

Well.. I'm pretty new to photography. I've Nikon D5100 with Sigma 17-70mm f/2.8-4 OS HSM and Nikon 60mm f/2.8 micro lenses. I'm interested in Portraiture and yes, both these lenses performed well. However, I'm planning to purchase a budget telezoom lens. I conclude into two, after verifying lots of reviews and those are
1) NIKKOR 70-300mm f/4.5-5.6G IF-ED
2) Tamron SP AF 70-300mm F/4-5,6 Di VC USD
Some says Nikon is better in class while others Tamron. So I'm confused in this matter. Please suggest me which one is better atleast in AF and IQ department?

I would be looking at the handling and general compatibility of my lenses. There is a lot to be said for using all one marque - the controls and handling will be the same and the compatibility with the maker's own cameras probably more assured.

On this basis, and in the expectation that Nikon do not make bad lenses, I would go with the Nikon.

I'm sure that the Tamron also performs well though, so why not visit a dealer and see how the two lenses fit in your hands? There is much more to a lens than other users' opinions and even tests and reviews.

John