reddit-detective VS Socialhome

That's what it is tho. You create a time-line filter that shows only posts containing those hashtags - is that not a subscription?

There are also more literal implementations for this like SocialHome [1] where you can click + on hashtags you like and public post with them appear in your home timeline

1 - https://socialhome.network/

* in case of a mute, it could also be not wanting their federated timeline to be flooded with primarily mastodon.social posts

Lack of federation between these instances and mastodon.social could be a reason not to pick mastodon.social. (Similar situation applies to mastodon.online btw, which is a spin-off server of m.s.)

Another reason to pick a different instance could be not wanting to use mainline Mastodon software. For example because you want to run your own instance on limited hardware (Mastodon can get a bit resource intensive), don't like Ruby, miss certain features, don't like the front-end (though alternative external front-ends to Mastodon do exist), or some other reason.

Personally I am on an instance that runs [Mastodon Glitch Edition, also known as Glitch-Soc](https://glitch-soc.github.io/docs/), which is a compatible fork of Mastodon which implements a bunch of nice features such as increased post character count (Mastodon defaults to 500 characters per post, Glitch-Soc supports increasing this in the server settings), Markdown support (though only instances that also support HTML-formatted posts will see your formatting; mainline Mastodon servers will serve a stripped down version of your post instead), and improved support for filters / content warnings / toot collapsing, optional warnings when posting uncaptioned media, and other additional features.

Another alternative Mastodon fork is [Hometown](https://github.com/hometown-fork/hometown) which focuses more on the local timeline (showing posts only from your own instance) with the addition of local-only posts, to nurture a tighter knit community.

Aside from Mastodon there are other implementations of ActivityPub which can still federate with Mastodon instances, such as [Misskey](https://github.com/misskey-dev/misskey), [diaspora*](https://diasporafoundation.org/) (which AFAIK inspired Google Plus back in the day), [Hubzilla](https://hubzilla.org//page/hubzilla/hubzilla-project), [Peertube](https://joinpeertube.org/) (focused on peer-to-peer video distribution), [Friendica](https://friendi.ca/), [Pleroma](https://pleroma.social/), [Socialhome](https://socialhome.network/), [GoToSocial](https://github.com/superseriousbusiness/gotosocial), [Pixelfed](https://pixelfed.org/) (which started as a sort of federated Instagram alternative) and more. [Fediverse.party](https://fediverse.party/) is a nice way to discover various protocols that make up the bigger Fediverse.