depends, if it's not "hot" stuff (that copyright owners will search and take down) the internet archive sounds good

torrents are gonna die if nobody seeds, soulseek needs you to be online for someone else to download

I think torrents are the best approach to this thanks to their decentralized nature. they can die if nobody seeds anymore but that doesn't mean uploading it on some site is gonna make it better as that site can go down too. Besides, if you have a spare laptop you can keep always plugged in and doesn't consume a ton, you can make it constantly seed your stuff.

I think personally the best approach is through torrents but that's how I see it. Do what you think works best

Soulseak, I find it the easiest. I use an app called Nicotine+

I recently found out that eMule is still alive and kicking.

Good old eMule.

The easiest way is emule. Just share the folders and that's it. There are other protocols that allow the same, but they have less users than emule users