I liked having an insurance broker. He was not an agent for any particular company. That way if the collision insurance from one company was cheaper, he could pair it with the liability insurance from another.

That being said, when I moved away from his office I signed up with esurance so I didn't have to drive two hours every time I needed to renew or something. For me, they had the cheapest rates, and I tried all the major companies. I don't have homeowners insurance, so I just have auto experience with them. We've filed three claims with esurance and I've never had a bad experience. Everyone I've talked to has been helpful. My policy auto renews and my payments are auto-debited from my checking account. And if you ever lose an insurance card, you can just print another one.
This reminds me I need to print one now. Thanks for asking this question!

It's a pain in the bum, but I'd probably just call all the major companies and get their rates. Do the same with a couple of brokers. Then rank them based on their rates and how comfortable you were with their customer service. I'd probably also leave your son off your insurance, but there is the chance that bundling all of it together could reduce his premiums. That's sort of a personal call though (how responsible is he, etc.).

I always find agents for this kind of thing since they get paid on the other end. You need to make sure it's not the kind of agent who steers you to where (s)he can make the most profit so ask the proper questions.