I use mautrix. It creates a matrix space where all your discord stuff goes, and within that it will create spaces for each server you manually choose to bridge.

DMs also go into a DMs space. DMs are bridged automatically, but each server you want has to be added with a command.

Looking at those three, appservice is old, and out of your element does not do puppeting (meaning it bridges discord-matrix chat rooms, rather matrix-discord accounts), making mautrix the best option IMO.

If you are looking to make a discord server you run accessible on matrix, out of your element may be better.

For using your own discord account through matrix, mautrix is the obvious choice.

I use the mautrix one in self bot mode. May get my account banned at some point but it seems to work well enough. No idea how well it works to merge a Discord server with a Matrix space, though.

Replies and emoji reactions work. Media uploads work too. It seems to ignore the file upload limit, though, so large images + non-nitro accounts may cause confusion.

It doesn't support some features (threads, notably) but I don't think many people will be sad about that.

Using Mautrix and appservice, both are good enough for me to talk to my Discord only friends and not have the app anymore