Technology

It really depends on your needs, like most things.

What are you trying to achieve? Just set up a place for folks to chat about a topic?

I'm inclined to suggest that if you're moving from Discord, then I suggest you pick a public server and create your room there. You already aren't self-hosting or getting bridging, so no loss. A public Mjolnir used to be on matrix.org but isn't anymore, so you have to be alert to spammers; if you have enough people you're willing to make mods, this is manageable. Matrix spammers tend to pop in, drop some fishing or advertisement; if you have someone watching 24/7 they can ban-and-remove the spam pretty quickly. Otherwise, you clean things up whenever you're in there; it's annoying, but not arduous. If you're a small room, you won't attract the spammers as much; if you're larger, I'd hope you have enough folks who can help mod.

I would not try to self-host out of the gate. If you do, start with a beefy server; you'll need a bunch of disk space - maybe not immediately, but as soon as one of your users joins a big room on a different server. I've only tried Synapse; you might try one of the other servers, but they'll all have the same disk space issue: it's a result is the design of the protocol.