Good question. I wish I knew myself. Sometimes, I change camera several times before I'm even out of the door :ROTFL:
The main rule is that I use the D80 when I need the extra resolution and the S5 for people and street. Since I have a vertical grip for the D80, I also tend to use it with heavy lenses. The D80 will also usually give better results with lenses of lower quality, like the Nikkor 70-300 ED. But the most important rule is this:
There are no rules. I try to get the best results with whatever camera I take.
I do prefer the S5 though, due to colours, WB, DR and a more "natural" look. If I have time, I will go back to the Motor Show with the S5 and hunt for more interesting shapes (and girls
).
For paid jobs, I usually bring both, both for backup and because I use them differently. In a controlled environment, particularly if I can use a tripod, I tend to choose the S3 over the S5 though. There's something about the files from that camera...
Did that make sense?