2,569 votesGraham Barker commented
Yes, yes, yes (please)! For me the lack of automatic sorting is my biggest irritation, and the main obstacle to me paying for Wunderlist. For defaults I would suggest:
1. Tasks with due dates - sort by the due date
2. Tasks without due dates - sort alphabetically
3. Apply the above to completed tasks also
(with the ability to be sort differently, or manually, as at present).
The lack of permanent sorting makes Wunderlist impractical for long reusable lists like grocery lists. I know the completed items are not listed randomly, but they may as well be if you've got no idea where to look if you want to un-tick something.
That's why I still use Google Tasks for my shopping list of over 250 items. The web app is poor and proper desktop apps are lacking (hence my need of Wunderlist for everything else), but there are good iOS and Android apps which have proper automatic sorting and sync with Google Tasks.
Examples - Google Tasks Organiser (Android) and gTasks (iOS) both allow permanent alphabetical sorting, both in active and completed tasks. If small developers of free apps can manage it, I'm sure Wunderlist can.
2,827 votesGraham Barker commented
I can see the usefulness of showing all subtasks, as suggested, but would emphasis the part about it being an option (which could be turned off) rather than just always on.