The Nikon will definitely be better. But at 3 times the price, it sometimes makes ppl re-consider.
If you have no problems with budget and you want the best quality, then go for the Nikon.
But if you're like me, budget strapped, then you can consider the Tamron as an alternative which gives decent quality and value for money (at it's budget level) But do check the lens if you get one as there are some lemons which have back-focusing problems.
Cheers,