I wear very flexible shoes (vivobarefoots). When walking on a flat and clear surface I strike near my midfoot/heels. My midfoot and heels tend to strike at about the same exact time.
When do I step on my forefoot?: When walking up or down hill, I strike forefoot. When walking on lots of small rocks (like in a stream or scree field) I step somewhat carefully on my forefoot so that I don't smash my heel against something. When I hike off trail and I am stepping on lots of fallen branches, I step on my forefoot. When walking around actual barefoot, which the skin on my feet isn't tough enough to do comfortably (i just do it around camp), I step on my forefoot because it's more comfortable walking on pokey leaves and branches that way. If I putting my foot down in between some bushes and I can't see exactly what I am stepping on, I go forefoot.
Basically, the more damage stepping on the ground will cause to foot (from tiny rocks or sharp branches), the more my foot naturally steps on the forefoot.
People don't naturally always step on their forefoot on flat ground. That's a myth that has been popularized by barefoot running shoes manufactures to push their products into casual use. However when running, it's always forefoot. Go watch Cody Lundin, a survival instructor who walks around the desert barefoot, and you will see him heel striking.
Also when I first started using very minimalist shoes I did more forefoot stepping on flat trails. Now I seem to walk more on my heels, probably because they are tougher now.