Which lens for a nikon d50 is best?

I mostly photograph nature, still life, and some portraits and i'm wondering which of these three lenses is best for those:

AF-S DX 18-55mm
Nikon AF Nikkor 35mm-70mm 1: 3.3-4.5 or
Tamron AF Aspherical LD 28mm-200mm 1:3.5-5.6

I would go with Nikon because Nikon camera's, imo, work best with nikon lenses. If I have the choice between those three I go with nikon just because I know nikon is great, and as a sidenote the nikon lense that you listed is probably the most easy-to-use out of the three.

You should go with Tamron AF 28-200mm F/3.8-5.6 XR Di Aspherical (IF) Macro Zoom Lens for Nikon Digital SLR Cameras

19.3 inch (0.49m) Minimum Focus Distance entire zoom range
1 - 4 Macro Magnification Ratio at f=200mm MFD 0.49m
Weight - 354 grams (12.5 ounces)
Diameter x Length - 2.8 x 3.0 inch (71.0mm x 75.2mm)
Accessory Flower shaped lens hood

For still life and portraits that nikon 35-70 is quite nice. Does a good closeup and is surprisingly sharp.

Recommend Tamron AF 70-300mm f/4.0-5.6
We purchased this lens for sports action shots. It's been wonderful, and we've gotten some excellent football shots. We chose it because it was an excellent value (lenses get expensive quick).

It's hard to find fault with this purchase.

Nikon 70-200mm f/2.8G ED VR II AF-S Nikkor Zoom Lens would be a nice option for you. Its most attractive features are:-
1.Fast f/2.8 Zoom-Nikkor lens
2.Nikon VR II (Vibration Reduction) image stabilization
3.7 Extra-low Dispersion (ED) elements;
4.Nikon Super Integrated Coating (SIC); exclusive Nikon Silent Wave Motor (SWM)
5.Focuses to 4.6 feet