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
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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.
@noellabo how to choose a mastodon server:
don’t, use pleroma instead 
@sophon I am often told by supporters of Pleroma and Misskey that I am writing this for Mastodon.
I use Pleroma... I'm using Akkoma right now, and I'm also running two public instances of Misskey while supporting the developers of Misskey and spreading the word about PeerTube and Pixelfed.
It's good to endorse products you support, but doing so out of context can hurt your image.
@sophon Yeah, I thought so! But there really are a lot of them...
@noellabo@fedibird.com @sophon@plma.plus.st I personally benefitted from your article for Misskey, I am grateful for that, so I am fully aware about your support to other projects. Fedibird is truly a splendid fork of Mastodon👍, therefore I understand you are in favor of Mastodon. My only hope is that people can use fediverse rather than Mastodon network, as such new comers would know it is not just a boxed "Twitter alternative" but a broader world with greater possibilities to be explored.
@noellabo ik I was semi-joking