By far the best task manager I have used, and I think I have tried them all... This one checks all the boxes I need:
1. Support for "Start Dates" not just "Due Dates" - right off the bat this leaves a lot of the other task managers out.
2.iPad/iPhone app. The 2Do app on my iPad is awesome!
3. Integration with the other apps I use. I use Airmail 3 for my work emails, and this is where most of my 'tasks" come from. I can "send" emails with a swipe straight to 2Do, and they are automatically linked back to the task in Airmail. So when I open the task in 2Do, on either my desktop or iOS device, with one click/tap it takes me back to Airmail and the original email. Perfect!
4. Active support and development. The developer is great, constant updates, bug fixes, and improvements. There are more than a few promising Mac task apps that might as well be abandonware, for the lack of support and updates they get...
Again, highly recommended!