The Gedo Mazo with all the tails since tails mean Power.
Shukaku=1
2 tails= 2
3 tails=3
4 tails =4
5 tails =5
6 tails = 6
7 tails = 7
Add up all of the tails together and that is 28 tails of power.The Hachibi and Kurama only equal about 17 tails of power. Kurama and the eight tails are strongest tailed beasts but the other 7 are still pretty strong, there's only one tail difference between the seven tails and eight tails, not to mention if u factor all the other tailed beasts in helping it.