In an ideal world I'd be going for the Nikon 70 - 300, but I can't afford it. After looking at a couple of reviews, the Tamron looks like a decent compromise though.
I have had both, I kept the Tamron, Tamrons VC is much better than Nikon VR in my opinion.I don't think the Tamron is a compromise, too me its a better performing lens after owning and using both lenses. You won't be disapointed with the lens.
Have a look at the last paragraph of this review. >http://www.photozone.de/nikon_ff/619-tamron70300f456fx?start=2