Generally, whatever is cheapest. For it isn't so much the brand or type of toothpaste that ensures good dental hygene and healthy teeth and gums, it is the daily practices of how and when you clean your teeth.
I haven't lost a tooth since I was eighteen years of age. I'm now seventy-seven. However, I did lose three of my adult teeth between fifteen and eighteen. Why? I put it down to drinking softdrink mainly, and not cleaning my teeth when I should have - mainly because of ignorance.
At eighteen I joined the Navy and there saw an Educational film that made all the difference to my teeth-health. The film was an old one; produced in World War Two. It mentioned that the Eskimos had no word or words in their language to describe tooth ache. Why? Because they never got tooth ache. And why didn't they get tooth ache? Because of their habit of chewing hard on such things as animal skins (to soften them) The hard chewing exercised the tiny muscles that hold our teeth in our gums, making them so hard and strong and deep that their gums never became soft and unhealthy.
Of course, that does not apply to today's Eskimos who have changed to our Western ways. Now, they do get gum diseases and tooth aches.
The other thing I learned from that film is that something like half of our tooth decay occurs within twenty minutes of our eating. So, always clearn your teeth as soon as you can after you've eaten. Oh, and forget things like chewing gum with its sweeteners or eating sweets. The sugar will cause tooth decay.
Go to your dentist once a year and get any tartar build-up cleaned off.
So, to sum up: clearn you teeth as soon as you can after a meal. Use something really hard and chewy such as a part of a rubber dog-bone or such and give it forty to sixty hard chews directly after clearning your teeth. It takes only a few seconds but will make all the difference between shelling out good money at the destist or being able to spend it on something you'd far more enjoy.