Are Tamron lenses better than Nikon's?

Or at least the 70-300 VC. I went to camera shop to ask about lenses and everything to get a sense of what I needed to start saving, and I originally asked for Nikon lenses, but the clerk steered me toward Tamron. I don't doubt the Tamron I'm speaking of is a good lens- I tried it out myself and he showed me shots from a promotional book taken with it - but he said Tamron is better and mentioned how they've been in business for quite some time. I've always been under the impression you should get lens from Nikon or Canon and I was surprised he started to try to sell me this. Just want info from more photographers.

Added (1). Yeah, I'd like to add when he started talking about how old Tamron was my first thought was "Nikon's a really old company, too."

The Tamron lens probably has more profit for the camera store.

Otherwise, they are not as good as Nikon lenses.

Having said that, Nikon did outsource a 70-300mm to Tamron once (Tamron built it with the Nikon name), but that lens is not the current 70-300mm lenses that Nikon sells.

I have seen variable reviews. Some say that a good sample of the Tamron 70-300 VC can be a little sharper at 300mm than the Nikon 70-300 VR. Some say that Tamron has a higher rate of disappointing samples.

3rd party lenses such as Tokina, Sigma and Tamron can be very good. The top end range of lenses produced by these companies can be as good as anything by Canon or Nikon.
BUT
The bottom range lenses, especially their 18-300 type lenses are barely average.
Nikon and Canon do not release details of their electronics to these companies so they have to reverse engineer their products (ie take a Canon lens apart to see how it works). This means that they miss features that are built in to future proof lenses.

example - I have a Sigma 28-200 lens that works perfectly on my old Canon film camera but they missed something iin their design so it doesn't work with my Canon digital.