personally I like to choose a short campaign. This way I am not pressured to conquer the whole map. It's easier to play slow when you don't have to take over the whole map. While it may easy to get te 20 regions, I won't destroy the factions needed for victory. Then, when i am ready to start a new campaign I just eliminate the faction needed. For example, as the moors take over a majority of spain and leave portugal with only one settlement. This way i can continue playing, but can also win when I feel like it.