cell phone coverage/good comparison web site

I am trying to choose between Verizon and AT&T for cell phone service in Los Angeles. I am only concerned about coverage and call quality (because my firm will pay :wink: ). So, if you have an opinion on AT&T v. Verizon, I’d appreciate hearing it. Or, if you know about a website that does these kind of comparisons, or a link to one about cell coverage in L.A., that’d be great too!