Get a Sigma 17-50 f/2.8 or a Sigma 17-70 f/2.8-4 Lens? A monitor vs a TV?

Should i get a Sigma 17-50 f/2.8 or a Sigma 17-70 f/2.8-4 Lens?
or is there something else you would suggest for my Nikon d5000?
I'm looking to get more light into my camera and a crisper image.

ALSO: a monitor vs a TV? For Photo work through my laptop.

Added (1). Better in low light is my main concern, a crisp image being second. I prefer to get in close with a lens vs wider too.

You could go with a 50mm f1.8 lens to get much more low light ability for just a fraction of the price, but if zoom ability is crucial, I'd go for the 17-50mm lens. If you're simply presenting your work either a TV or monitor will work, but as far as editing and retouching goes, you'll need the monitor instead of TV. Have fun.

I would go the 17-50 f2.8 because that will be better in low light. If you're at 50 on that lens, and 50 on the 17-70 lens you'll be at a constant f2.8 on the 17-50, where as on the 17-70 you might be on a f3.5. Thus making the 17-50 a better choice. I would use a monitor for colour calibrating purposes.