There's certainly nothing wrong with going down the 3rd party route and some lenses offer excellent bang for the buck. Indeed, some 3rd party lenses out perform OEM lenses
(Nikkor 12-24 Vs £300 cheaper Tokina 116). I own a Tokina AT-X Pro 28-80 f/2.8 which I'm happy with. Its AF and focus speed are bang on and fast and stopped down to f/4 and below gives nice crisp images.
I also own a Tamron AF SP90 macro lens. Optically, its excellent. Mechanically, its an absolute dog. Its slow to focus and the AF on it seems to have a mind of its own on occassions. Compare it to my dad's Nikkor 105mm VR, and there is no contest. The Nikkor blows Tamron away in terms of focus speed, focal accuracy and build quality but, its double the price of the Tamron.
All OEM and 3rd party manufacturers have made some fantastic lenses in their time. They have also made some real pigs ears. Without knowing what type of lens you are looking for, we can't offer you suggestions on what is the "best" for you.