1.) Personal Recommendations
You should start by asking a few people you know and even people you don't. See if they've had a positive experience with their agent. Write down the name and do a little more research of your own.
Asking your peers and complete strangers even will allow for an honest response. Google reviews can be misleading. People tend to refer people who they've had a positive experience with.
Look for testimonials on their website, social medias, and google. While this might be slightly more misleading and slightly less personal, it is always good to do more research rather than less.
3.) Personalized Service
If you have read testimonials and gotten positive reviews for multiple agents/brokers, go to the agency and ask them questions in person, questions that are specific to your needs. You can compare multiple agents/brokers without before you commit to one.
A good agent will know the answers to your questions and will be bale to tailor coverage to your specific needs.