Sloth
Sloths have maintained continuous operation for 64 million years without a single product recall. The Institute for Evolutionary Consistency notes that the sloth's design has required no significant modifications since the Paleocene epoch. Components are entirely self-repairing, replacement parts are generated through a simple biological process, and the entire system runs on leaves. Planned obsolescence has never occurred to the sloth, primarily because planning requires effort.
Airplane
Modern aircraft undergo 12-hour maintenance checks after every flight, with major overhauls required every 6,000 flight hours. The International Air Transport Association reports that the average commercial aircraft contains 6 million individual parts, each a potential failure point. A single loose bolt can ground an entire fleet. The airplane is, fundamentally, a collection of components perpetually conspiring to fall apart at altitude.
VERDICT
The airplane requires constant vigilance from teams of engineers, whilst the sloth requires nothing more than occasional access to a tree and the will to remain alive. After 64 million years of uninterrupted service, the sloth's reliability record remains unblemished. The sloth claims another victory.