If you don't care about it, then pen and paper does seem to be ideal, but smartphones have a major advantage of portability.
For me, every extra object in my life is a source of stress. Something that can be lost, along with all the information, in a list with no cloud sync.
Paper is fine around the house, for non urgent things, that I'll probably remember again next time I actually see the problem I made the list entry about, which is probably a pretty big fraction of the stuff people use lists for. Perhaps I should try a paper list for that one of these days.
But if there's any chance I might want to take something outside.... cloud sync is amazing. It does majorly create a pseudo productivity trap, and a temptation to check a bullshit notification(Made a little more manageable by Keep tiles on a smart watch), and probably is not optimal for getting stuff done.
But it sure is convenient not to have an extra item to carry.