Available everywhere — iOS, Android, Mac, Windows, Web, even Apple Watch. Natural language input ("buy milk tomorrow 3pm #groceries") is best-in-class. Karma system gamifies productivity. Best for: people who live across multiple devices.
Built-in Pomodoro timer, habit tracker, calendar view, Eisenhower matrix. TickTick packs every productivity methodology into one app. Best for: users who want one app to replace several.
Apple-only, and unapologetically so. Things 3 is the most thoughtfully designed task manager on the market. Its "This Evening" and "Anytime" separation is genius. Best for: Apple-only users who value design and UX above all.
Multi-platform → Todoist. All-in-one → TickTick. Apple-purist → Things 3.