I suppose it depends on the product or service you are building, doesn't it? e.g. A writer would benefit more from Twitter whereas someone who is selling Notion templates may benefit more primarily from YouTube for showcasing the product but then also use Twitter to explain their design thinking process and cross-promote.
It is difficult to say which social network is best for building a loyal audience. as different networks are popular with different groups of people and what works for one business or brand may not work for another.
From just an observer's perspective I feel like it's Youtube. For example, I feel like people with large followings from all other social platforms eventually try to do Youtube, while the opposite direction isn't as common.
I think there is something about evergreen content and the difficulty of creating long form videos that earns you very loyal followers. Most other social networks in general require far less work to create content by comparison.
I've been able to build a loyal audience on TikTok in a relatively short space of time - but it depends on the type of audience / content you're discussing
For me it’s been newsletters. The inbox is a personal place and creating relationships there to me a reflection of good content that people commit to consuming.
That commitment signals loyalty. They’re not just giving a second to read, they’re diving in. It’s a 2-way commitment that allows for the relationship to really prosper.
Hope that helps!
Vikara