While other Misskey forks are trying to get away from Misskey like Iceshrimp which is doing a full C# rewrite and dropping the Misskey API for better or for worse.
Sharkey will always stay Misskey based in fact we even try to work together with the Misskey team and Misskey Devs like @kakkokari_gtyih, and maintaining compatibility is key, our goal is to make an "Improved Version" of Misskey not our own entire fedisoftware, and we also don't plan to move away from being a SoftFork of Misskey and most importantly as part of this comes the fact that in the case something were to happen to Sharkey you could easily move to Misskey upstream without many issues
So if you are looking for drastic changes you should be better off with Catodon(Mastodonifyed Misskey/Iceshrimp) and Iceshrimp (can u even call it a misskey fork at this point if they're rewriting everything?)
But if you are looking for Misskey, but with much needed improvements and guaranteed ability to go back to Misskey if shit hits the fan, Sharkey is best for you, we don't plan on majorly changing everything about Misskey, we are just making improvements to Misskey that the community requests and if possible we try to work with the Misskey team and sometimes even upstream our changes