hi gibss,
I usually prefer heavier lens because like what others says, counter balance with your body as well as countering your natural handshake. I'm using a 1 series body for canon, so if I have a lighter lens, I will have to hold my camera body to shoot and only fingers to zoom, focus if its a lighter lens. A heavier lens allows me to have 1 hand on the body and the other on the lens. So it kind of helps in the overall holding feel.
So in those scenarios, depending on what brand you are using, an IS or VR on the body for the lighter lens should give you better results. Eg. sony. But if you have a heavier lens on a lighter body and you need to hold the lens, then it make more sense to have the IS, VR on the lens.
At the end of the day, usually the longer or/and heavier lens will have IS or VR, which is why Nikon latest 16-35 VR lens brings about a lot of discussions in the Nikon forums asking is there a need for VR in a wide angle zoom.
If you realised, the camera companies usually makes the overall balancing and feels optimized for the bigger bodies and top of the line lenses. Like 1D + L lenses. And the latest IS, VR technology are usually on these lenses as well.
Hope that helps
