Running or walking which produce most health benefits
Walking is very good low impact exercise that even people with very low fitness level can engage in. Walking is good for maintaining basic fitness level. But there are certain wrong assumptions about walking like walking can reduce weight. But many people who start walking with the hope of reducing body weight get almost no results. Actually walking can contribute to weight loss only if the walking session can increase the heart rate to 60% –70% of the maximum heart rate. So to get benefits of your walking time you will need to walk fast.
But one word of caution just do not try to increase your walking speed in one day specially if are not used to it. You need to increase speed gradually over a period of couple of weeks. Every day start your session with slow pace than after 15 minutes try to speed up. But do not put too much effort you need to do it easily. If you feel brisk walking is putting too much stress on your body you can walk every other day.
Those who are with high fitness level or can easily walk 4 miles within an hour can engage in running. Running is better if you want cardio respiratory conditioning. In fact all the benefits that one can have from brisk walking can be gained from running. But the problem with running is it is not a low impact exercise, so if your joint health is not great you may have trouble running. Also there are more chance of injury if your running posture is not correct or if your running shoe do not support your feet properly.
So comparing everything it can be said brisk walking is the best bet for all.