I've tried a ton of similar apps—Things, Omnifocus, 2Do, TeuxDeux, Workflowy, Weekplan, Flow, TickTick, Asana, plain text to-do, and even the newer ones like Plan (getplan.co). And I still find myself going back to Todoist every time.
I don't know about the others but these things are very important in my workflow:
Speed. Todoist's fast. It captures and manages tasks at the speed of thought. Want to tag? Press @. Want to categorize? Press #. And don't even get me started on the inline date parsing feature. Others don't like it that much but I enjoy it.
Cross-Platform I switched from iOS to Android and can still use Todoist. The Android app is probably one of the best Android apps out there using Material Design.
Customization I like reading workflow pieces from other Todoist users. But at the same time, I invested some time trying to figure out what set of labels and filters work best for me. It always helps to match these to how you're actually managing tasks. The color-coded task categorization is also a big plus.
Just Enough Features I like Todoist's thoughtful simplicity. Though I think it's missing a calendar similar to Flow or TickTick, I still think it's better than those two. I tried them for a week or two and still find Todoist superior.
But if you're looking for a task collaboration app that you can use with a team of 3 or more, you might want to check Flow or even Asana or other apps.
P.S. Todoist just released a business edition though I haven't checked it.