S.M.
I attended high school in Plano and my daughter is enrolled in Denton ISD (this would be your school district if you move). And my mom lives in Savannah. So I actually think I can help you with this since I know about both locations. If your number one concern is schools - don't move to Savannah. Plano schools are very much superior to Denton ISD schools, I am sorry to say. If I could afford to move to Plano to my kids in those schools, I would be there in a second. The elementary and middle schools that your kids would attend are not bad, but Denton HS is not the greatest. Certainly not as good as Plano high schools.
On the other hand, Savannah is a very nice community. It has a great pool, nice people. The small-town feel. But it is quite a ways away from everything. You would have to go to Little Elm to do your shopping. But it's definitely a buyer's market out there right now because of the fact that home prices have severely dropped.
A lot of pros and cons. It's a big decision. Good luck