This is an odd one for me as currently my favourite Streamers to watch are Nickslots, Jimbocasino, David Labowsky and LetsGiveItASpin.
But I watch them for all different reasons: Nick I watch the most (just more down to his streaming times than anything else), you can see his heart is in what he does and he's always up for some good banter and silly jokes.
Jimbo also has good banter but he seems just really lovely as well. I suppose the best way to describe the two, Nick is the kind of guy you'd buy a pint for. Jimbo is the kind of guy who would buy you a pint. That's the sort of feeling I get from him.
David is just so chilled and relaxing to watch, always so cheery, always smiling and it's a joy to watch. A bit like if Bob Ross did slots instead of painting in my opinion.
Finally LetsGiveItASpin as already stated, have people to bounce off of, lovely guys and always having good fun.
So for me, it's about being genuine, being able to have a bit of a laugh (even at your own expense), not taking things too seriously and making your streaming environment a very accessible place.
Interesting to note, the streamers I mention while there is a lot of things that are spoke about or discussed (shows, current events etc). I have noticed that these guys tend to stay very a-political and that makes viewing so much nicer for everyone involved. There have been some streamers who I've caught who make a mention of one side of political affairs or another and because of it, I'm put off by what they've said or on the flip side, I'm rooting for them but then can see others aren't so happy so if you're broadcasting your personal beliefs and political stances, you are going to have a fall out from one side. I'd advise NOT doing that and keeping staunch beliefs to yourself but if there is an important topic happening, there are ways to comment on it and have a healthy discussion without saying whether you're for/against whatever it is.
So yeah, genuine personality, able to have a laugh, keep politics out and engagement with the people who are watching you are the most important things I would say to have a healthy broadcasting stream. It also helps immensely if you have a voice like David's that makes you feel safe and comforted as you watch.