If you're having a hard time choosing between several appealing possibilities, don't fret. Pick the possibilities that are easiest to develop and move on. You can always supplement your world with a new location built on an entirely different hook at a later date. For instance, if you're having a hard time choosing between a world dominated by dragons (opposition hook) and a world dominated by Wizards (class/race hook), go with the dragons. Later, you can introduce a separate continent ruled by Wizards. In fact, every time you introduce such an area you have an opportunity to devise a rationale that connects its hook to your other hook(s) and adds depth to your game world.
Returning to our example, let's suppose that, across much of the world, all the most important rulers are dragons and that most wars and international affairs stem from conflicts or alliances between these dragons. While humans can rise to the rank of duke or baron, they are ultimately little more than slaves or vassals of the dragons. Eventually though, the players discover a large hidden island in the middle of a vast sea. This island is ruled by Wizards, the ancestors of whom successfully rebelled against the dragons and established their own secret kingdom more than a thousand years ago. The Wizards' ancestors defeated their reptilian masters by stealing the secret of magic from them. It turns out that every human Wizard in the world ultimately owes his ancestry or tutelage to an inhabitant or former inhabitant of the island. Working together, these two hooks have just provided us with some rich backstory and fodder for future adventures. We now know how mankind learned the art of sorcery, and we can suppose that at least some of the dragons are interested in finding the island and recovering magical treasures stolen long ago.
