When comparing Toodledo vs Teuxdeux, the Slant community recommends Toodledo for most people. In the question“What are the best cross-platform task apps?” Toodledo is ranked 23rd while Teuxdeux is ranked 59th. The most important reason people chose Toodledo is:
It's possible to create a to-do item by sending or forwarding an email.
Specs
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Pros

Pro Can create to-do items via email
It's possible to create a to-do item by sending or forwarding an email.
Pro Decent filtering and sorting
Pro Priority organizing
Pro Great GTD implementation
The GTD principles are very perfectly supported by Toodledo.
Pro Functionality-rich
Integrated sharing, note taking, habit tracking, and outlining make this a more powerful tool than a simple list of to-dos.
Pro Upload From CSV
Quickly upload an excel (CSV) file template of tasks to a folder for complex but repeating projects.
Pro Well documented, free-to-use JSON API
If you adopt Toodledo as your productivity system, you can be confident that you can extend it to fit your needs with this programmatic access.
Pro Can tag items
Pro Space to add lengthy text
Notes area that can then be hidden.

Pro Sends a daily email reminder
Toodledo reminds you via email of the tasks on your plate for the day.
Pro Apple Watch support
Integrated support for Apple Watch lets you check on your to-dos on the run.
Pro Fast, easy to use interface
On desktop, tasks are assigned to a single line. To see the full description, you can hover over that task. Editing can be done by double clicking, and re-ordering the events are as easy as dragging them around.
It also supports markdown - a common web formatting tool that allows italics by putting single asterisk () around words or phrases, and bold can be done by using two (*) before and after the phrase you want to be bold. It can also handle links by putting the text you want visible in square brackets, and the link in round brackets so this: [Slant Homepage](https://www.slant.co] would look like this: Slant Homepage
Pro Very focused, allowing it to be the best at one thing
Instead of trying to be a both a calendar and to-do app, it focuses much more on the to-do aspect. There is a calendar view, however your tasks aren't organized by time - just by order. You can reorder the day's events, and if you don't get them done they will automatically roll over into the next day, so you can be sure that you aren't ever missing anything.
Cons
Con Free version limited to 20 folders
Con Android app has annoying notifications
Whenever the app fails a background sync action for any reason (server issues, lack of internet connection, etc.), a notification appears.
Con Good as a starting point
Toodledo is a good starting point, but is essentially the same as an Excel spreadsheet where you have to build your workflow via the saved searches.
Con Subscription based will cost money each month
Instead of a single time purchase, Teuxdeux costs $3 each month, or $24 for a full year. There is a free 30 day trial, so at least you can try before put any money forwards, but a one time fee - even if it's $10 - is cheaper in the long run than a few dollars each month.
Con No Android support
