Walk-around lens for a Nikon D50?

Any suggestions on a good walk-around lens? Looking towards the Sigma and Tamron lens. Do not have the money for the Nikon lenses. I just sold my 18-55 NON VF kit lens. I only have a 50mm/1.8.

Also a second question to this is - can you tell me the big difference of a 17-50to a 18-50 to a 24-70. I know that they all deal with ranges but does 17, 18, 24 make a huge impact?

thank you in advance. - beginning recreational photo enthusiast.

Added (1). I forgot to mention - what I would use it for mainly would be landscapes and portraits. I'm more into the sharpness of the lens - preferably a lower than a f3.5

I'm not a Nikon guy but Canon. I use Canon's 28-200 as my main lens - it's excellent. I don't know if Nikkor has the same size but I'd bet they do.

17-24mm is quite a stretch if you want wide. Nikon's first 24-85 may be for you. I;ve used a 28-105 as my walkaround lens for quite some time, wonderfully sharp

I'd look for a 28-70mm lens. Remember on a D-50 that is going to be a 45mm to 105mm lens because of the cropped sensor, The thing is that a lens for a D-50 is going to be more, because of the AF factor, no motor in the camera body. But you can always just focus by hand. Look for used lenses also, you can save some money on those. I'm still using a Nikkor f/4 500mm lens that I bought in 1993 at a pawn shop on a D-2H. Those lenses still sell for over a grand used. But they are really sharp lenses.