What I do with a lot of domains I'm interested in, is doing a Google images search, I like to see it in "pictures", businesses using terms. Did that with law billboard, lawyer billboard, attorney billboard. Just a quick glance, it seems the city + lawyer/attorney search numbers above are pretty accurate. Looks like attorney gets used just a tad more. I don't think you can go wrong with either term really. I think they like using attorney better because sometimes lawyer might be a little negative, think of all the lawyer jokes.