I have only just started the game and I do not know enough about the map to make the best decision. Which is the best territory to pledge to at the start of the game?
The pledging system is just a way to progress the story with some basic control given to you. You actually end up pledging to every single territory. You are just being asked to decide the order. The order makes no difference really but when you hover over, it will tell you the recommended level. Pick the territory that has a level that is closest or lower than your own. If you pick an area too high, you will likely have some trouble killing the enemies here.
At the start of the game, you will have minimal options. So go with the flow. This decision is not one that will have any impact on the game at a later stage. You will not turn one territory hostile if you side with one over the other.