I use Todoist for my own things, and Trello for collaborative things.

I really love Todoist. It's really simple to enter tasks -- extremely low friction with browser extensions and Android widgets, etc. It has all the features I want in a tool like this -- simple tasks, sub tasks, categorization, tagging, attachments, recurring tasks, prioritization, and apps/widgets/integrations galore. And it's free, or cheap for the pro version (I do pay, like $50/year).

It also gives great flexibility with a simple query language to create custom views/filters. Like work tasks due in the next 3 days, etc.