For me its the content, plain and simple. This can include an original post or a comment they made.

It needs to be insightful, relevant, thought provoking. It doesn't necessarily need to be my way of thinking, in fact giving me pause and making me consider different viewpoints is something I really look for in people I follow. I already know what and how I think, why follow someone saying the same things I do? 

I like to learn things so I tend to follow people who post new and interesting things, not just cat memes or pic of flower with no description, I can google those if I want.

People who make me think, engage me in philosophical discussion or debate. The ones that can help expand my horizons so to speak.

These are the individuals I tend to follow the most