It depends on what you want to do in the future.
If you are serious about photography and likely to upgrade cameras within the next few years, then if you have the funds, go for the Nikon.
The cost is a big factor, but replacing a defunct lens if you then switch to full frame later on is even more expensive.

If money is a big issue and you're happy with a DX lens, then I don't think you'd go far wrong with the Tamron, they do make some good lenses.
If you crank up the ISO then your shots should be reasonable if noisy inside, (unless you use flash of course)

edit....
if you're after a Nikon F3.5 instead of a 2.8 then I would edge towards the tamron/sigma