A few weeks back, I began to use Things 3 as my main task management app (or simply my to-do list app). Before that, I was using TickTick, which is also a great task management app!
What I like about Things 3 is its simplistic UI, accompanied with the suitable organisational features for me, and the great user experience.
First, the UI is so clean and so simple. One look at the app and you should understand.