It's like having a *@gmail.com vs a *@yahoo.com email address.

Any instance allows you to send/receive email (or that is, browse lemmy).

If your instance goes down for whatever reason, you'll not be able to access that account.

Simple answer is it does not really matter, everything is connected and most things can be reached from anywhere.

Slightly more complex answer: each server instance (e.g. lemmy.ml, lemmy.world, lemm.ee and any others) has its own rules and regulations, dictated by the individual admin(s). You should read them to know what the instance is about, its general philosophy, and if it is a good fit for you. From this also follows the fact that your instance admins can choose to disconnect from other server instances - in that case you can not reach anything from the other instance. An example is many nsfw-free instances disconnecting (‘defederating’) from porn instances like lemmynsfw. Or disconnecting from right-wing troll instances.

So, the general answer is it does not matter much, but there is some fine print to it you should be aware of.

lemmy.world and lemmy.ml are different "instances" of Lemmy. Anyone can host one, and every Lemmy instance can talk to other Lemmy instances, and similarly any other software using ActivityPub. It's part of the "Fediverse", or the federated universe.

In the long term, it won't matter unless lemmy.ml starts defederating from other instances or other instances start defederating from it. "Defederating" is a term for when the admins of an instance choose not to talk to another specific instance.

Someone else will be better at explaining the why but no, it doesn't matter. You can still see and do the things.

I'm on the connect app from .world and reading your comment just fine!

I like the soft bounding box UI around each post on this app the most.

It doesn't matter, all that means is you created an account on a different instance/server that can access content on .world, it's the same situation the other way around, .world to .ml instances. It takes a bit to get used to it but after a while it just starts to feel like Reddit but with more meaningful conversations. I have an account on both instances in case one goes down I can still access the same content, that's the beauty of the fediverse.

Well, those are different servers, basically speaking. As for a user it actually rather won't be matter what to use. I made it oversimplified, but seems about right.

They're just different instances, hosted by different people. You can make an account anywhere and still have access to everything, so from that perspective it doesn't really matter. You picked one of the major ones, so you're fine :-)

The big difference is deciding who you trust with your account. Who are they? Anybody can host an instance, after all. Will they keep your details secure? Will they be around for many years, or will they close down and you lose your account after a year, two... three? What's their ability to withstand hackers and attacks? How good is their server infrastructure to ensure a bug free, speedy experience? Etc.

I just figured the big ones will hang in there one way or another, I find the people running the .world instance to be very transparent about how it's run, and the issues they face running it.

That said, I wouldn't store any information in my Lemmy account that I don't mind being hacked or leaked, just in case.