I use a variety of task lists every day. Many people might want to use only one app for all their tasks - but I've found it to be unrealistic, and possibly impractical. I've become comfortable using various different platforms to manage my different activities: some work better than others. Here is my low-down.
Asana was my favourite (I've since moved more processes to Trello). The UI isn't the best, even after their "flat" update", but I once watched the founder of Asana use it in a video and despite the complicated UI, it's actually easy to use.
The pros for me: tagging, user assignment, easy to add tasks, task sectioning and the cute, little project dashboards. It has a nice little integration with Harvest for time tracking and many more integrations. It is also widely adopted.
The reason I eventually settled on Asana was despite its flexibility it still retains a nice Now, Next and Someday methodology.
Podio is a very flexible system, and I use it with some clients. It's advantage being in being easily tailored to suit your needs. There is also a marketplace, where others customise a series of "apps" to create a workspace (for example a Sprint set of apps which quickly setup a Sprint Workflow application; or a Marketing Campaign Planning suite of Apps).
It's flexibility can also be its weakness, as the learning curve is quite high.
Trello is a particular todo app: In its simplest form you have three lists: To Do, Doing and Done. I never understood the "Done" board - but I guess some people will find it useful - at the very least as inspiration that you are working through your list.
Trello works like a Sprint, and is used widely in Software Development. Open Trello boards, such as that of Ghost Foundation, invite the public to contribute to the boards.
Trello is useful for roadmaps, and versioning.
I use it for collecting ideas and sorting them, more than as a work-through-the-list Task app.
Things is my Benchmark Todo list: thanks to its GTD methodology of Now, Next and Someday, and a pleasant and rapid interface (The app runs native on devices). The downside is there is no web app. So I can only access it through my phone "on-the-go" and sometimes this is not what I want.
iPhone Reminders and Todos
I used iPhone's reminders and todos for personal stuff.
I was working with Evernote for a while. It has task lists, and integrates well with my Evernote workflow. I've stopped using it however, all my stuff is on Trello generally.