I used to walk more, mostly because it's compatible with photography, especially unplanned stuff like street/candid and found-object photography. But for several years after a car wreck I needed a cane to walk any distance. That tended to hinder spontaneous photography until I switched to lightweight P&S cameras that I could operate one-handed.

But for exercise and the sheer pleasure of moving I much prefer bicycling. Since resuming riding a few months ago I wonder why I waited so long to start again - other than that pesky poor balance and cane thing, which I suppose could have been resolved with a recumbent trike. Long walks felt more tiring than invigorating. Bicycling feels more invigorating, and I usually have a burst of energy after a relatively brief rest.

I still take lots of photos during bicycling ventures, but it's less compatible with street/candid snaps around the city. Great for my rural routes, though. I stop whenever something catches my eye, and ride alone so I'm not holding anyone up.