Hidan: A follower of Jashinism; essentially the slaughtering of lives and utter destruction was the nature of this religion. That is what gave him his power, in order to keep living forever and retaining immunity to certain death injuries, he must keep praying to his God, keep performing his rituals and keep taking lives in the most brutal fashion!
Kakuzu: To have been the only Shinobi who fought Senju Hashirama and lived to talk about it almost or over a century later, is the man with five hearts. A unique and forbidden jutsu that only he could perform, allowed Kakuzu to escape death by forcefully ripping out the hearts of other humans while keeping them conscious. A cycle he continued by replenishing his supply of hearts over hundreds of years.
Sasori: The master puppeteer; who chose to become his own creation. By retaining his own heart in the same canister that supplied his one of a kind poison, he was free of the limits by which normal humans are bound; disease, fatigue, injury......and death!
Orochimaru: The forbidden jutsu that was mastered by a single ninja from the Leaf. The Immortality Jutsu! Although, the same cannot be achieved for the victims of this jutsu, who lose their bodies, as well as their lives, when Lord Orochimaru takes over them! Moving from body to body by these means, he lives on.....
But that is not the only ability he possesses, for a white snake symbolises RENEWAL! Every cursed seal ever placed by him, retains a little part of him. The only catch, is that he must be revived by his own followers........
Uchiha Madara: Whether by his own choice or not.....he was brought into this world when Yakushi Kabuto summoned his soul through the Edo Tensei. Though Kabuto is incapacitated, Edo Madara is not! The only means to be erased, are being sealed away.....but for this to be done, one must rival the awesome and unending power of this Uchiha God, which is an impossibility in itself!
So then.......which one do you like? Don't pick your favourite ninja, just the method of staying alive!
say what?!