Depends on your weather and size of land. Most (not all) apples need a cross-fertilization. There are even cross-grafted trees available, with several types of apple on one trunk, to get cross fertilzation with a single tree. So if you only have a back yard, go for a pair of dwarf apple trees. If you have a bigger place, go for more small trees, or few big trees, your choice. Also note, our trees often show biannual variation, good year, bad year, etc.
The dwarfs are less able to handle heat and drought, but much easier to harvest.
Note though, that apples and crabapples can cross fertilize fairly successfully. So even if you have a single tree you may still get fruit from it, depending on your neighbors landscaping. Trees from seeds are definately not the same as the parents. But if you have room to experiment you may develop the next great breed. Or just have a dud. Thats why nearly all are grafted.