Waterfall's strength is predictability when requirements are truly known and stable, since everything is decided in advance. Its weakness is that software requirements usually aren't stable, so problems and changes surface late, when they're expensive to fix.
Agile's strength is adapting to what you learn from real feedback, delivering working pieces early and often. Most modern software uses an agile or hybrid approach, because building the wrong thing perfectly is the more common and costly failure.
Updated July 2026