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TIL, thanks for letting me know!

Lemmynsfw.com is quite large and purely dedicated to NSFW content.

Yes, it does make a difference, but like with many other things you should not fall into the trap of decision making paralysis.

Your current instance lemmy.world is the largest and perfectly adequate for the majority. It also costs nothing to make accounts on other instances and is done in less time than it takes to decide between them.

That said some reasons to choose one instance over another:

Federation with other instances

Some instances choose not to federate with others. Common reasons being political ideology or NSFW/piracy/violent content. Others might be more liberal and leave it up to their users to block whatever within their own apps. As someone already mentioned world seems to have defederated dbzer0 the piracy focused instance. Some political instances that often also get defederated are the far left ones like hexbear and Lemmy grad (seems like those are defederated by lemmy.world as well).

Server location and performance

Especially country focused instances like lemmy.ca or feddit.uk will have their servers in their own countries. You can of course access them from anywhere, but a European user might have a better time choosing an instance with servers located in Europe, while someone in America might have lower latency with one located there.

Alternate frontends

If you are accessing Lemmy through a browser rather than an app, you might enjoy alternate frontends that change the design. Your current one lemmy.world for example offers 4 different designs that can also be found in the sidebar alexandrite, photon, voyager mobile and one looking like old.reddit.

General ideology of the instance

Your choice of instance might also tell others something about you. If you choose a country specific instance people seeing your profile name might assume you come from there, if you choose one with a particular political view people will probably assume you hold similar views. Same goes for other instances that are related to things like sexuality or hobbies.

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That’s pretty much me aswell, besides that I didn’t even spend energy to try and learn others. Simple docker compose, simple ui and easy way to add services.

I am sure there are alternatives that allow for more elaborate setups and fancier things. But for the low effort I put into it, I got a page with some nice buttons with appropriate icons that scales to whatever screen size it’s displayed on. Only additional thing I did was enabled to show some basic info to see if e.g. SABnzbd is downloading something, which was also super easy.

Existing one or on a topic of my choice?

If I had to teach an existing one it would probably be sport, since as a reasonably fit person with a decent understanding on how to train in a healthy way it would probably be the one where I could come closest to providing a similar level to a real teacher. Otherwise maybe sociology? Think I could do a decent job there aswell.

If I could make my own it would probably be personal finance. Because I think here in Germany education on this topic is basically non existent. And there is so much money wasted on bad financial products and wrong decisions, that giving everyone some basic lessons would have a huge positive effect.