When comparing Riot vs Discord, the Slant community recommends Riot for most people. In the question“What are the best messaging apps for Android?” Riot is ranked 1st while Discord is ranked 14th.
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 User friendly
Discord follows the same type of interface design popularised by Slack, which is extremely clean and attractive, and doesn't clutter the interface with unnecessary chrome and cruft.
Pro Free for unlimited users
Unlimited amount of users.
Pro Can be used in browser
Users can invite others to join a Discord channel via a web link, which means no installation is required to use the software - which is one of the big typical barriers to entry for social software.
Pro Easy setup
You can quickly send invites to people and they can join in using the web client without having to create an account or install the app.
Pro Good 1-click invite system
Discord allows inviting people to a specific channel with a link. Links can be set to expire. Low effort/passive invite mechanics.
Pro Open source bots and management tools
Discord has a wide variety of bots for things from airhorn noises to automated server management, to leveling systems for chat. The bot API is open and there are dedicated sites for finding bots.
Pro Game integration
Discord shows which game each user is currently playing, which among other things helps users to form PUGs with minimal hassle.
Pro Has low-latency VoIP support
Pro Supports video and text communication
Behaves and looks like Slack for regular text channels, but with the ability to create voice channels as well
Pro Android app has push notifications
Pro Familiar for Slack users
For those that are used to the way Slack (a similar chat client) works, Discord will be familiar in its use, which lowers the learning curve quite a bit for those that have switched or tried Slack before.
Pro Low effort invite mechanics
Pro DDoS mitigation
Discord prevents users from being DDoSed out of games.
Pro Numerous controls for setting member roles.
Deny access, Deny write message, Allow read messages etc.
Pro Targeting of roles
Targeting roles allows for quickly requesting someone from a group e.g. artist, moderator, etc.
Pro Ability to thread channels
Ability to create channel categories for channels to sit inside of.
Pro Ability to create bots
Discord provides an API for creating custom bots.
Pro Friendly payment policy
Free account have no tangible restrictions.
Premium account is just a way to say "thank you" to developers. And it work for all servers of discord (not as in slack). And it can be purchased by one who wants. In contrast to Slask, where all active members of the server should be "premium".
Pro Language localization
Have localization for many language, including Russian.
Pro Dark theme out of the box
Pro Syntax highlighting and Markdown support
The support is limited but still exists. It's a killer feature for dev teams.
Pro Does not allow NSFW related things to be posted unless in a NSFW channel
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 Proprietary software
Discord is closed-source, meaning their code isn't available for inspection or reproduction
Con No self-hosting avaliable
Discord is wholly hosted by Discord (the company), you cannot run private instances, and all servers are hosted on their infrastructure. For most people, this won't really impact their usage.
Con Developer's previous company was sued for privacy violations, among other things
Con Based on Electron = eats a lot of ram
Con Some functions cut out and available only with "Nitro" subscription
Con Very unstable on Linux
Con Not a generic "team chat" tool
All the UI and the features are aimed specifically at communicating with your gaming team/clan.