my family's had state farm for a while, rare to file a claim but it's usually been easy. nice that you can call your own agent instead of a call center. i've used mercury before, it was a bitch to sign up, and never filed a claim so wouldn't know how that goes.
i like aaa though. some guy totaled my car once, his insurance was aaa. they were fast, nice, and gave me a really good deal. i've heard that from others too: when shit happens, aaa gives you a good deal.