First timer... nearly overwhelmed. How do you pick?

I've read up. A lot. Think I know what I want now and when I look at providers, there is a list of about 20 different companies for the specific plan/area I'm in. Does it matter which company? If the coverage is supposed to be the same no matter the company, why would I pick one that wasn't the lowest cost option? Is there a way to rank companies somehow? A/AA/AAA etc.