Longevity
Gandalf Wins
Gandalf
As a Maiar spirit, Gandalf predates the creation of the physical world itself, having existed in the Timeless Halls before the beginning of time. His current form in Middle-earth represents merely the most recent of potentially infinite incarnations. He has already survived death once, returning as Gandalf the White with enhanced powers. By any reasonable measure, his lifespan extends to approximately fourteen billion years and counting, with no obvious expiration date.
Sloth
The individual sloth survives between twenty and thirty years in the wild, which seems rather modest until one considers the species' remarkable staying power. Sloths have inhabited Earth's tropical regions for approximately sixty million years, outlasting the dinosaurs' extinction event and numerous ice ages. Their survival strategy of extreme energy conservation has proven more robust than the aggressive approaches of countless extinct predators.
VERDICT
Personal immortality spanning the age of the universe surpasses even sixty million years of species persistence.