In regards to witnesses... what I do is research each witness. Just because they are in the top 20 doesn't mean they do projects that you would support or like.

The best place to get the names of 400 of the witnesses is here
https://steemian.info/witnesses

I would go to their pages, read about what they do, projects, who they support, what is their record, etc. You can always change your mind too. Just because you vote for a witness doesn't mean it's forever.

Months and months ago there was a scandal about a witness- who has since left the platform... so do your research.