I switch up my task manager every now and then to stay on top of what is out there, but for the vast majority of the past four or five years, OmniFocus has been my todo app of choice.
Free downloads: OmniPlan and OmniFocus for iOS are free to try - The Omni Group:
The first, OmniPlan 3.6, features a better dark theme and optimized inspectors, designed to reduce the number of taps required to manage your project. Weโre also transitioning OmniPlanโand OmniFocusโto free downloads. Both updates contain a free 14-day trial; the Standard and Pro features are unlocked (and discounted for existing customers) via In-App purchases.