Thanks for asking!
I'd say I'd like them to honest, with integrity, caring about Steemit and it's users and wanting to do all they can to create a better world through Steemit.

Regular posts on their opinions and what sets their soul on fire to do good!
Interacting with authors and building a strong community.

Now I'm new to Steemit, so maybe that's not the role of witnesses. I find all the nodes and technical stuff so complicated, I'm looking for caring people who want to interact! :)