I would go for f/2.8, however if its f/2.8 IS then it'll be the perfect combination! IS' effectiveness is also dependent on the maximum aperture of the lens. If it's say f/5.6 at the farthest end then IS won't help much in low-light conditions. However, a constant f/4 IS is more useable compared to f/3.5 - f/5.6 IS especially when zoomed in. Hope I make sense here
- capable of thinner dof, can isolate subject from background better compared to a smaller aperture lens ( depending on what you are shooting )
- can potentially shoot under lower lights handheld ( depends on settings )
- can increase shutter speed and freeze motion
but expensive, heavy ( usually )
* the 2.8 glasses ( especially for zooms ) are usually the higher end offerings of the companies. The IQs are usually better.
- some handholding advantage as well especially dimmer lights
but expensive, and comparing to a larger aperture, while you can afford a slightly slower shutter speed, there will be some motion blur depending on ur subjects.
Draws abit of power as well.
* there is a limit to how much VR can save ur shakiness
I am trying to decide between at 18-200mm VR and 17-55mm f2.8 actually. Thanx for all advise. I know its very different lens, but I actually seldom zoom more than 70mm, though the 18-200mm is very versatile...
Depend on situation
I find indoor or low lighting condition, wide angle prime and VR lens are very useful and recommended. So far my best lens for indoor is 70-200 IS. I could easily get sharp shots @ 1/60sec.