Most of what I’ve read (combination of running message boards, articles and blogs) recommend not being up on your toes all of the time. Your heel should touch (or “kiss”) the ground lightly before lifting your feet again. Like anything else, though, everyone’s natural form is going to be a bit different. The above feels the most natural and comfortable for me (my problem is I think about it too much and don’t just walk/run) and being up on my toes and balls of my feet the whole time just feels off.