- Matrix is for now (like Discord) more of "slack like" service alternative (but has potential to become more than that).
- Telegram might be the easiest to use where you likely find the most people but I disagree with a lot of things done by/around telegram.
- Threema (now open source) is as far as I know the most privacy focused one and by far my favorite. I like the way they are doing many thinks and they have many small goodies (like you can give a small "thump up/down" to messages in 1-to-1 chats from the message received notification to indicate agreement/acceptance). Or the way they handle accounts (separate from phone number and license, you can give people your Threema id without giving them your phone, the "trust levels", etc.). Or that they have a clear&clean business model. There are also a bunch of aspects which are useful if used in a e.g. business context like account revoke-ability, in person QR code based key exchange, fixed chat history etc.
> Matrix is for now (like Discord) more of "slack like" service alternative (but has potential to become more than that).
More specifically, I would say Element (the most popular Matrix client) is more of a "slack like" alternative, but most other mobile Matrix clients are much more WhatsApp-like.
Most of my contacts (tech-oriented, Europe-based) are using Threema and I am most happy with it, especially because I do not have to share my phone number (or complete address book!). And the new video call capability is also working well. Unfortunately, most of the family is WhatsApp only. Since I will not use anything Facebook, they either have to use SMS or contact me via my wife.
- Telegram might be the easiest to use where you likely find the most people but I disagree with a lot of things done by/around telegram.
- Threema (now open source) is as far as I know the most privacy focused one and by far my favorite. I like the way they are doing many thinks and they have many small goodies (like you can give a small "thump up/down" to messages in 1-to-1 chats from the message received notification to indicate agreement/acceptance). Or the way they handle accounts (separate from phone number and license, you can give people your Threema id without giving them your phone, the "trust levels", etc.). Or that they have a clear&clean business model. There are also a bunch of aspects which are useful if used in a e.g. business context like account revoke-ability, in person QR code based key exchange, fixed chat history etc.