I have Tamrons along with a nikkor. Tamron's SP series is top notch. All the pics I took at the Milwaukee Zoo were with a Tamron SP 28-75 2.8. Pics here.
Sigma and Tamrons are the top 2 aftermarket lens manufacturers. Tony, Canon and Nikon both make their own lenses. Promaster & Quantaray usually are either rebranded Tamrons or sigmas. Nikon makes its own glass also. I believe Tamron and Sigma get theirs from Hoya (so I heard).
A couple of the budget Nikon's are rebranded Tamron. There was a big bruhaha a few years ago about Nikon changing the specs and drawings of one of their posted lenses because someone noticed the drawing (3d view of all the elements) was exactly the same between a Tamron and Nikon on their web pages.
Most of the world uses Hoya glass, Nikon and Canon included. I'm not sure how much of Nikon glass is still made internally. I'm not sure if they even have a team that hand grinds glass anymore.
As for 3rd party lenses. If I had to choose, I'd take Tokina first. Though Tokina's gear is starting to look dated on paper because Tokina has no AF-S nor VR features. Tamron, has some Nikon features like AF-S due to the reason mentioned above. Sigma is left to reverse engineer many of the Nikon features, and often mucks it up. If you do a little research you'll hear about people having to have their Sigma lenses "Rechipped" to work with some new Nikon body, feature, or even firmware. This is again because Sigma is left to reverse engineer all the features so as not to have to pay Nikon a license fee.
I've owned Tamron, Sigma, Tokina, Vivitar, and I'm sure other (MF lenses) Nikon mount lenses. Even though Tokina is behind in features, I'll always look to them first. Their regular line is as well built as Nikon's Pro lineup (minus AF-S and VR). In fact, Tokina is founded by Nikon lens crafters who went out to form their own company...something that doesn't happen often in Japan.
Sigma is known for making some really fantastic Pro lenses to fill gaps that Nikon has in their lineup. Like the 30mm f/1.4 that I have, or the Sigma 400-1000mm
Tamron basically has traditional focal lengths and makes some Pro-ish lenses. They seem to be concentrating their efforts on *sharpness* since that's what the average joe can pick out of a photograph...and they do hit their mark pretty hard on a couple lenses.
Build quality I'd take Nikon/Tokina, then Tamron, followed by Sigma. Sigma has some fine Pro-level builds. But because of their backwards engineering and spotty QC, I have to knock them down a notch.
Really though, all that rambling said...when you need a lens, you have to look at what focal length and features you need, then do some research as to who can give you what you need at a price range you can afford. My Sigma 30mm f/1.4 is a good example of that. The closest thing out there is the Nikon 35 f/2, and that just wasn't fast enough for me. So Sigma it is. Another example; I needed a Macro lens for my electronics photography. It needed to be up to medical/surgical quality, and I didn't feel Nikon had that. So I had to track down a Tokina lens built in the 70's. To this day, Nikon has yet to make a lens as sharp and detailed as this lens from the 70's (which was designed on super computers of that era).
So figure out what you *need*, then hone in on the models that do what you need, then research what *real* photographers say about those lenses in *real world* use. Reading the specs and looking at charts only tells you maybe half the story.
Oh, and I like turtles.