Mathematically it makes sense to pay down large balances first. This is because most of the monthly payment tends to be interest and not principal. So, paying down the principal on large balances snowballs the paydown effect faster. But, we cannot forget about the psychological impact of making a quick win. If you can pay one mortgage off very rapidly, it motivates us to work harder on the next milestone. So, it may work better for you individually to start small and work your way up.