I had a company provided Verizon phone for about 3 years, then switched to Cingular when I left that company about a year ago. I went Cingular because the plans fit the wife and I better (not data users, not a lot of minutes).
I’ve been perfectly happy with Cingular. Verizon had a real bad dead spot in my house that doesn’t seem to exist with Cingular so that’s a huge plus, but that doesn’t mean Cingular won’t have a big deadspot right in your living room. Generally both seemed to have good coverage, but I did get more dropped calls with Verizon. Your results may vary.