The "best company" depends on where you live, because not all carriers offer plans in every state.
Best plan would be the one that offers most benefits that are important to you at the lowest price.
All the sites you have mentioned are licensed online agents. Best site would be the one that is easiest to navigate for you & has friendly, informed licensed agents.
I take a non-biased approach when it comes to these types of questions. Let's hope that another member who has had first hand experience will respond to you too.
Whatever you do, run your thoughts by a licensed agent to make sure you are on the right track!
I can tell you that I been going back and forth to ehealthinsurance and I am still deciding on what to get. I like that site because they don't force you to enter a number and email to get the information. I like to research myself then be able to talk to someone if I want to. I like the idea of being able to order online too.
I not tried the other sites or seen anything simuliar yet but look forward to any other suggested sites.