If you are staying longer than 10 days and you want to go to parks every day, then you'd need an Annual Pass. A 10 day pass is the most number of days you can purchase. Honestly, even if I was staying 11 or 12 days, I would probably just go with a 10 day.
However (there is ALWAYS a 'however'), if you are staying 10+ days, and paying out of pocket for meals, and plan to eat at TS every day, it might pay you to get a Tables In Wonderland card. It costs $100, but it will give you 20% off your entire meal, including adult beverages at most restaurants.