When comparing Todo.txt vs Joplin, the Slant community recommends Joplin for most people. In the question“What are the best cross-platform task apps?” Joplin is ranked 5th while Todo.txt is ranked 9th.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Easily editable format
Todo.txt can be edited in plain text and then displayed with neat styles.
Pro Editable from any text editor without needing any proprietary software
Because todo.txt is just a todo standard with various compatible apps to edit it, you can update it from any device as long as it can edit text and you can access your todo.txt file
It's convenient to be able to access your todo list quickly via your programming environment so you don't have to switch contexts, and to have a separate todo.txt file per project.
Pro Works with lots of apps for every platform
Todo.txt lists can be edited in virtually every text editor ever made and accessed on devices that support Dropbox. The user community has also created a number of apps for dozens of platforms.
Pro Command line support
You can edit your lists using the command line (e.g., Terminal) via a supplied bash script.
Pro Full control over your to-dos
You have full access to the underlying programming rules, and therefore total control over your task lists.
Pro Extensible
Has been extended to include most things people want, including a multiple of interfaces and app for all platforms.
Pro Easy syncing
Todo.txt automatically and seamlessly syncs through Dropbox.
Pro Wide range of interface apps
The community has developed a wide range of apps that interface with the basic file structure. These apps vary in how much they accomplish, how much hand-holding they do, their level of glitz, etc. They range from plugins for an editing app like vim to stand-alone, platform-specific GUI's. So YMMV depending on what you use. (todopy is particularly nice, a Python program that has a "console" mode which provides a keyboard-driven GUI.)
Pro Follows the unix philosophy
Does one thing: to do lists
Pro It's free
It runs on MacOS, Android, and Python (in the Mac's Unix CLI) -- all for free.
Pro Easy to sync up between lots of devices and interfaces
At a bare minimum you just need to be able to edit text, but there are many apps and advanced interfaces you can install on many devices to supplement your to-do list editing.
Pro Offline access
Pro Open source
Peace of mind that there is no malicious piece of software in the app.
Pro Encryption
Pro Cross-platform
Supports Windows, Mac, Linux, Android and iOS.
Pro Supports file attachments
Pro Supports markdown
Pro Supports tags for notes
Pro Web Clipper
Browser extension saves full pages, clean content, or screen selections to new notes.
Pro Optional CLI interface
Provides a CLI interface for terminal lovers.

Pro Supports multiple languages
English, French, and Spanish, Italian, German, Czech and many others.
Pro Active user forum with support from app creators
Support, troubleshooting, and new feature requests are easy to make at the user forum and you can contact the app creator directly.
Pro Dropbox support
Can sync using Dropbox.
Pro Nextcloud support
Pro Timed alarm reminder for to-do lists
Cons
Con No support for reoccurring tasks
Tasks have dates corresponding to creation and completion, but there is no explicit support for due dates or for tasks that reoccur.
Con Nested tasks not supported
Many todo tasks for developers end up having sub tasks that need to be performed for a parent task to be completed, but the todo.txt format does not have any nesting.
Con Android app not updated since 2013
The app only seems to support Dropbox. It would be nice to see support for different and newer file storage services.
Con Sync issues with Android
If update on Linux then sync on Android, sometimes the Android sync will duplicate or remove some journal notes. Seems to be a bug in the Android app. The Linux app alone without sync with Android seems to work well using Dropbox. But don't expect changes you make on Android to sync properly back to Linux.
Con Sync issue under Linux
The Linux client has a bug that requires the user to click the mouse frequently in order for sync to proceed. This bug has been open for a while.
Con Gargantuan memory footprint
1GB+ of memory for taking notes.
Con Old school interface
Con Bloated
This project is suffering from feature creep and uses a lot of memory for a note-taking app.
Con App Image launches very slowly
On Linux, you can only install via App Image, which take 5+ seconds to launch. I can launch LibreOffice in under two seconds.
Con Sync issues on Windows
No way to change account settings and sync easily corrupted.
Con Weak tag searching
Joplin can currently only search for a single tag at a time. None of the boolean operators (AND, OR, NOT) are available for use in searches. This greatly diminishes the usefulness of tags in Joplin.
Con Can't create tags from the mobile app
