In the last year I've become more of a runner in the suburbs than a walker in the suburbs. This has its good points and its bad points. In the plus column, I exercise a little more rigorously and finish a little more quickly.
In the negative column, well, I'm not walking. And walking sets the brain to spinning. It's about the pace. The clip-clop instead of plod-plod. It's about exerting one's self enough to jostle the gray matter — but not so much that huffing and puffing is all I do. Walking gives me a chance to notice things; with jogging I might run right past them.
The best days are when there's time for a run and a walk. One for the body and one for the soul.