Just about every camera company has added image stabilization to their line of cameras or lenses. The implementations vary, but the objective is the same; make images sharper when taken at lower shutter speeds by minimizing the effects of camera movement.
The question is, is a faster lens better, or worse than a slower lens with some form of stabilization.
Motion: The enemy of sharpness
There are two kinds of motion that can blur images, camera motion, and subject motion. Camera motion is the little bit of rocking and shaking the photographer makes when standing still, the vibration induced by the mirror flipping up, or any number of small movements and vibrations that happen to the camera while a photo is being made. While the movement may be imperceptibly small to us, to the camera and lens these movements are actually quite large.
Subject motion, on the other hand, is just that, your subject moving around on you. You could also lump into subject motion the relative motion of the subject and photographer if the photographer is moving. While not exactly subject motion, its effects are the same.
Of all the motions that can affect the sharpness of an image, the image stabilizer can only affect one of them, camera shake. Specifically it can only reduce vibrations in the plane of the sensor (i.e. up-down and left-right) and in some cases tilt. Moreover, the stabilization system can only correct relatively small motions.
In short, the stabilizer can reduce some camera shake and that’s it.
Aperture: More Light, More Speed
The aperture on the other hand controls how much light can reach the sensor. In this case, we’re looking at maximum apertures, since they let the most light in. More light, in a similarly light environment, means exposing the film for less time (i.e. increasing the shutter speed).
The practical result of shorter exposures is less motion of any kind.
Looking towards the Future
Ultimately, the question might become a moot point.
Digital camera sensors and noise reduction algorithms are improving every year. Today’s ISO 12800 is as good as yesterday’s ISO 1600. Further, as the technology is refined, the number of lenses that can have stabilization systems is increasing; and that’s not even considering the cameras with in-body stabilizers that stabilize all lenses. It’s certainly possible that in a few years, the only choice will be between a fast stabilized-lens and a slow stabilized-lens.
In Short: Which way to go
Image stabilization is not always a substitute for faster shutter speeds, especially when the subject is moving. While an image stabilizer will help improve sharpness of static objects at all shutter speeds, at least when hand holding, it won’t stop a moving subject at all.
The million-dollar question is do you shoot moving subjects in low light or not?
If you do, you’ll probably be better served with a faster lens, even if it’s not stabilized.