While State Farm's shopping experience is well-reviewed, customers did not feel as strongly about it's claims handling process. The company scored about the same as the other four large companies, but was still mediocre. A large national company may be expected to not be very efficient because of the various departments involved in handling individual claims. If you want the assurances guaranteed to you by a large, "legacy" carrier, then State Farm is the best to go with.
We can help you figure out if you need rental car insurance. The short take: If you don't have auto insurance, yes, you most likely need coverage. If you have robust car insurance, you might simply need a collision damage waiver as it’s the only way to ensure you won’t pay the rental company any damages in case of an accident. Of course, it gets more complicated from there. For the long take on car rental insurance, head here.