If I have to actually vote, it would be Kushina, because of her flexibility and versatile to play with many teams.

I do have BT Kakuzu, probably cheapest in the server too, when God of Luck smite on you. My total cost so far is 18k coupons, (that included 4 stars and bt), maybe cheaper than Naruto 6p for some players too.

I love playing him. But simple debuff such as blind can mess up your team easily.

Immobile, Chaos, and sleep can be controlled failed, but blind though. -*-

EDIT not completed BT, but +2 Chase and Passives