When comparing Roll20 vs Discord, the Slant community recommends Discord for most people. In the question“What are the best software tools for playing tabletop games over Internet?” Discord is ranked 2nd while Roll20 is ranked 4th. The most important reason people chose Discord is:
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.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro There's nothing to download or install
Roll20 is a web-based application that can be run in any modern web-browser making for an easy and quick way to get all players up and running.
Pro Easy access to character sheets inside of RPGs
You can view your character sheets, and make rolls by clicking on various skills and abilities on the character sheet. You can cast spells by clicking on the appropriate parts of character sheets.
Pro Has a whole backlog of premade RPGs
Pro Free
It's free as long as you don't need too many features, otherwise you have to subscribe.
Pro Easy to control what players can see
With any subscription ($5/month) on the part of the GM, Dynamic Lighting can be enabled. This allows players to only be able to see what their characters should see, without any management by the GM. Light boundaries must be set up beforehand, or you can buy professional maps.
You can use fog of war for free, which has simple controls.
Pro Very easy to create 5e character sheets
Charactermancer uses SRD content, and any purchased modules to turn character creation into a multiple choice wizard. No need to type in the text of spells or abilities, the weights of objects, or calculate your armor class. This is all performed automatically.
Pro You can make whatever RPG you want
Pro Very easy prep for D&D 5e
Wizards has created purchasable modules for nearly every published fifth edition adventure. These are set up and ready to go, if you know how to use Roll20. There are additional 3rd party submissions available for purchase or for free on the marketplace.
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 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 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 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 Numerous controls for setting member roles.
Deny access, Deny write message, Allow read messages etc.
Pro Ability to create bots
Discord provides an API for creating custom bots.
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 Dark theme out of the box
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 Android app has push notifications
Pro Syntax highlighting and Markdown support
The support is limited but still exists. It's a killer feature for dev teams.
Pro DDoS mitigation
Discord prevents users from being DDoSed out of games.
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 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 Does not allow NSFW related things to be posted unless in a NSFW channel
Cons
Con Laggy
The Roll20 interface is a little bit more sluggish than it ought to be.
Con Not 3D
Roll20 is a strictly 2D, top-down view tool.
Con Proprietary software
Discord is closed-source, meaning their code isn't available for inspection or reproduction
Con Based on Electron = eats a lot of ram
Con Some functions cut out and available only with "Nitro" subscription
Con Developer's previous company was sued for privacy violations, among other things
See:
http://classactionlawsuitsinthenews.com/class-action-lawsuit-complaints/openfeint-green-international-privacy-class-action-lawsuit-complaint/
https://www.ftc.gov/enforcement/cases-proceedings/closing-letters/openfeint-inc
Discord's privacy policy also states that while they might not sell your data, a company they get sold to will quite possibly attain said data and thus may be in "more" shady hands.
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 Not a generic "team chat" tool
All the UI and the features are aimed specifically at communicating with your gaming team/clan.