When comparing Riot vs Tox, the Slant community recommends Riot for most people. In the question“What are the best cross-platform & encrypted messaging apps?” Riot is ranked 1st while Tox is ranked 5th.
Ranked in these QuestionsQuestion Ranking
Pro Uses Matrix, the open communications protocol
Pro Supports text, voice, video
Integrates with Jitsi for multi-party video chats
Pro Web and mobile (iOS, Android) versions available
Pro Bridges to other networks
You're not confined within Riot's or even Matrix garden, and you don't have to make users of other networks switch to Matrix.
Pro Widgets support
Want to watch that flick at YouTube and discuss it at the same time? Have Grafana graphs stacked above your DevOps team chat? Collaboratively edit Google Docs and chat over without switching applications? This is possible with Riot.
Pro Very good and simple interface
Riot has a very simple interface, adding the ability for more unexperienced PC-Users to use it.
Pro Privacy focused
Tox uses military grade encryption and works completely peer-to-peer.
Pro Free and open source
The code is licensed under GPL (may change in the future) and is available on GitHub.
Pro Multiple front-ends for multiple platforms available
At the moment there is no official Tox client, but a selection of 32 and 64 clients for Windows, OS X, Linux and Android is available.
Con Still in active yet early development
There is clearly a User Experience issue esp. in web version which the developers are aware of and are working hard to improve. They've got the concept concrete, so UX won't be an issue in no time. Most often used parts are functional, but some are yet not.
The success of riot depends on how fast the development is, or it'll get outdated too quickly as developers of Signal and Telegram have predicted.
Con Early stages of development
Since Tox is relatively new, it has important features missing (like group video) and requires a proper code review before it can be deemed reliable and ready for everyday use.