How would the Sigma 17-70mm f/2.8-4 DC Macro OS HSM Lens, and the Canon EF-S 17-85mm f/4-5.6 Image Stabilized USM SLR fair for this type of shooting. Think of like an episode of 24. [\quote]
Brian I woudl still take the Tamron 17-50 or the Canon 17-55 because they are constant aperture 2.8. With the Sigma 17-70 and Canon EF 17-85 your aperture will step down as you zoom.
For video I would must rather have constant aperture over Image Stabilization. For me the only exception to this rule might be for very long 200mm and the like zoom lenses.
I have a Sigma 18-200mm f/3.5-6.3 DC OS which does have IS, but is a variable aperture lens. this is fine for me as I tend to sue very long lenses in good light like outside, so the loss in aperture isn't a huge deal for me.
If I had the money though I would opt for a 70-200mm f4 or f2 IS lens form Canon. Although, Sigma has a new 70-200mm IS lens that just came out and is a little cheaper than the Canon.
Too bad Tamron hasn't made an offering for IS in their long lenses yet.
Thanks for the advice.
The Tamron is a bit pricey for me right now.