When comparing car insurance, generally the biggest companies can compete better on price, perks and availability. But big brands spend a lot on advertising to stay top of mind, so keep in mind part of your premiums go to pay for a corporation and its advertising machine.
On the flipside, smaller, local companies tend to have better customer service with or without agent help, and you might find they offer unique perks and rates for your region since they're not spreading their risk across as many states. But if you ever move states, you might need to switch car insurance too.