Been using Apple Notes for 8 years now and can't imagine using any other tool at this point. Everything else is too complicated and with distracting thrills, or is too barebones. Notes is the perfect balance, and I like that the notes can be totally offline.

The only thing that needs improvement is the search function.

EDIT: Another thing I really like about Notes is how notes can be password protected, which includes full encryption, and they can be unlocked with your fingerprint. If the user doesn't interact with the app for a few minutes, the notes automatically relock themselves. This is great for journaling because I can be confident that the more candid thoughts I express won't be accidentally read by anyone.