Choosing a Mastodon server is ultimately a matter of trust in the operator.
The server should be in line with the purpose of your activity and preferably in the country or region where you live.
How to choose a Mastodon server
==
Mastodon is designed to be a decentralized social network, and it's strengths come when it's decentralized.
I'm sure you've always thought that choosing the most well-known, popular, and popular service would be a good choice.
With Mastodon this is not necessarily the case. Rather, there are many cases where it is better to avoid such servers and choose a medium-sized server, or a smaller server, or your own server.
The more users Mastodon's server has, the more effort and money it takes to maintain it, but it's not designed to make money, so the balance is getting worse.
Mastodon's answer is to divide it into smaller parts and manage smaller parts in order to solve the problem of large-scale services like Twitter, which are becoming too big and causing various harmful effects.
Guys, don't get discouraged if mastodon.social is slow. The solution is to move to a medium sized server that works better!
@noellabo@fedibird.com This applies to ALL fediverse platforms, so in terms of SNS don't limit your choice to Mastodon, there are also Misskey 
, Pleroma 
, Friendica 
, GoToSocial 
and more, they can all talk to each other with different favour of UI and UX, just look around.
Fediverse is designed to be decentralised, self-hosting if you can, put your data in your hands. Don't know how to do it? Check out https://fediverse.express , it is a good means for the beginners.