The best app for personal productivity is the one that lets you get more done and fits with your unique style and workflow. That being said, Todoist and Wunderlist are great options if you need a simple, shareable to-do list. Trello is great if you find the Kanban method more convenient. Finally, great productivity is sometimes about documenting your thoughts and ideas and organizing them into a searchable catalog. For that purpose, Google Keep can be really helpful.