I was insured with Zenith via the AA, but didn't find out how appalling they were until I had to make a claim.
Most of the staff that I had the misfortune to deal with were surly and incompetent, they entered the wrong information, asked me the same questions more than once, managed to lose my record and then 'found' it again. They didn't keep accurate details from information I'd provided and never rang when they said they would. I was constantly having to chase up and still am.
Incredibly stressful and frustrating, I would never use them again - or, for that matter, get insurance through the AA, as they were no help whatsoever.