I have separated the answer in terms of the operating system.
Top 5 To-Do List for android-
1- Microsoft To-Do, 2- Wunderlist, 3- Todoist, 4- TickTick, 5- Any.do
Top 5 To-Do List for IOS (apple)-
1-Apple Reminders. 2-Any.do, 3-OmniFocus, 4- Things 3, 5-Due.