Think of instances like Quarters, or neighbourhoods.
So, its really nice if you can find a neighbourhood where the local discussions matches your interest. Many years ago, I started in an instance I liked because of their URL. 
If your instance isn't interesting enough, you can always follow accounts and hashtags which will feed to your "home" stream.
Don't worry about instances, often, it's not very hard to move from one instance to another, if you end up choosing something else.
Welcome to the Fediverse!