probably a "real" apple tree. Most apple varieties are created by grafting a branch of an existing variety onto a new tree. Thats why despite genetic variation, they taste pretty much the same.
It's not my experience that apple varieties in the grocery taste "pretty much the same." Maybe you meant something else?
Apple trees are grafted because the best-tasting varietals don't form the most hardy root system. You put the good-tasting apple tree on top and the hardy strain on the bottom (to become the roots)
Each variety tastes the same (a golden delicious apple tastes like other golden delicious apples).
The grafting does that among other things "Maintain consistency". A hardy root system that you mention is one.
I started looking into it because my dad has a giant apple tree thats much bigger than the ones I've seen in an orchard, but the apples taste surprisingly bitter.
I guess another reason they like grafting is the trees stay smaller and its easier to pick the fruit.
https://en.wikipedia.org/wiki/Grafting