Not really. One of my lenses is a Tamron and the others are Nikon. A lens is a lens and you'll get pictures from any lens you put on the camera. The Tamron and Sigma 17-50mm 2.8, 28-70 2.8, 24-70 2.8, and 70-200 2.8 lenses are all really nice and if anyone saw the photos you take with them, they wouldn't know any different. I know lots of professionals who use Tamron and Sigma lenses because they are a lot cheaper than the Nikon versions, generally.
If you want a quick and dirty way of thinking about the other brands, here's what I do: Sigma focuses faster than Tamron usually, but Tamron lenses are usually optically superior to Sigma ones.
That being said, I've had bad Tamron lenses and great Sigma lenses. I've also had bad Nikon lenses. Each lens is unique. I'd advise you to stick with Nikon if you want the absolute best quality, or check DXOMark.com to see how certain lenses rate on your camera. They're a great resource.
If you want my advice for two lenses, a wide one and a telephoto, I say get either the Nikon 12-24 and the Tamron 70-200 2.8, or the Tamron 17-50 2.8 and the Nikon 70-300 AF-S VR or Tamron 70-200 2.8. For the most professional looking photos and most versatility when shooting, you want 2.8 lenses, but it's not completely necessary if you don't want to pay that much.
I hope I haven't confused you haha.
If you want a quick and dirty way of thinking about the other brands, here's what I do: Sigma focuses faster than Tamron usually, but Tamron lenses are usually optically superior to Sigma ones.
That being said, I've had bad Tamron lenses and great Sigma lenses. I've also had bad Nikon lenses. Each lens is unique. I'd advise you to stick with Nikon if you want the absolute best quality, or check DXOMark.com to see how certain lenses rate on your camera. They're a great resource.
If you want my advice for two lenses, a wide one and a telephoto, I say get either the Nikon 12-24 and the Tamron 70-200 2.8, or the Tamron 17-50 2.8 and the Nikon 70-300 AF-S VR or Tamron 70-200 2.8. For the most professional looking photos and most versatility when shooting, you want 2.8 lenses, but it's not completely necessary if you don't want to pay that much.
I hope I haven't confused you haha.
JNPhoto Workstation
(17 items) |
JNPhoto Mobile Workstation
(13 items) | 
Some photography
(26 photos) |
| CPU | Graphics | RAM | Hard Drive |
|---|---|---|---|
| Intel Core i7 2635QM | AMD Radeon HD 6490M | 16GB DDR3 | Western Digital Caviar Black 500GB 7200RPM |
| Optical Drive | Cooling | OS | Monitor |
| 8x SuperDrive DVD+/-RW DL | Integrated Heatsinks/Fans | Mac OS X 10.8.latest | Glossy 1440x900 LED Panel (Samsung LTN154MT07) |
| Keyboard | Power | Case | Mouse |
| Apple Chiclet Keyboard | Internal Battery/85W charger | MacBook Pro 15" Unibody | Glass Inertial Trackpad |
| Audio | |||
| Integrated 2.1 audio | |||
| View all | |||
|
JNPhoto Workstation
(17 items) |
JNPhoto Mobile Workstation
(13 items) |
Some photography
(26 photos) |
| CPU | Graphics | RAM | Hard Drive |
|---|---|---|---|
| Intel Core i7 2635QM | AMD Radeon HD 6490M | 16GB DDR3 | Western Digital Caviar Black 500GB 7200RPM |
| Optical Drive | Cooling | OS | Monitor |
| 8x SuperDrive DVD+/-RW DL | Integrated Heatsinks/Fans | Mac OS X 10.8.latest | Glossy 1440x900 LED Panel (Samsung LTN154MT07) |
| Keyboard | Power | Case | Mouse |
| Apple Chiclet Keyboard | Internal Battery/85W charger | MacBook Pro 15" Unibody | Glass Inertial Trackpad |
| Audio | |||
| Integrated 2.1 audio | |||
| View all | |||
Ditto on JamesonNorths post about used gear. You really cant go wrong with it, the only part I've bought new is my grip 
