- free large file upload (max 2GB), - native (non-electron) app for all the desktop platforms, - custom stickers (and not so limited as reactions on Discord, anybody can use any sticker set anywhere) - nice bot api (discord offers quite good experience as well) - works well when on shaggy mobile network. Doesn't send duplicate messages/etc (Messenger does) - doesn't censor messages. I'm free to send link to any website, upload any file type (again, looking at you, messenger) - you can quickly summarize different media shared in a given conversation, view all photos, movies, files, URLs, etc - search actually finds stuff (looking at you again, messenger) - you can be logged in on any number of devices (phew, WhatsApp)
Probably there are more. I'm so happy that most of my friends switched.
* Native Client Support - all of their clients are OS native, and perform quite well compared to their peers.
* Desktop and Mobile Parity - the desktop and mobile clients are equal quality, and functionality, which means it works just as well on my desktop as it does on my phone.