My friend Marius Masalar writing for The Sweet Setup:

It’s remarkable how much nuance exists within the concept of task management.
Over the years, we’ve seen multiple apps emerge to tackle this problem. Some are heavily focused on a particular methodology such as GTD, while others cast a wider net, catering to all sorts of workflows.
From that vast array of options, I keep coming back to a stalwart few that have proven themselves to be capable, thoughtful, and genuinely helpful in the pursuit of a more productive, organized life: Things, OmniFocus, and Todoist.
The only way to properly assess these options is to dive in and spend a long time using them; they need to flex to accommodate both the busiest and calmest times in my life.
What follows is not an attempt to crown a winner — it’s an examination of how these equally-compelling apps compare in long-term use. The goal is to highlight the strengths and weaknesses of each in a way that makes it clear which is the best fit for your needs.

Long story short:

  • Things 3, generally speaking.
  • Todoist for collaboration and cross-platform support.
  • OmniFocus 2 for customization and robust task management.

There are a number of great GTD apps out there, but these three are undoubtedly the best available. If you’re looking at the list and wondering where you fit, I’m willing to bet you’re not the only one. Marius does a great job breaking down the biggest features (and areas for improvement) for each app in this.