When the first iPhone came out I was almost more excited to get away from Verizon than the phone itself, and happily paid my contract cancelation free.
I really do not understand why there are so many people who prefer Verizon over At&t.
I was with Verizon for nearly 5 years and it was horrible. They nickel and dimed me on everything, and commonly overcharged me for data plans and features I never even used (they charge an entire minute of data usage even if you only use a single second). Not to mention they crippled all their phones Bluetooth capabilities, and then forced the phone manufactures into using the same Verizon created UI which made Windows 95 look state of the art.
To make matters worse, they have horrible customer service. Their reps have no authority to do anything to your account even if they made mistakes, and if you actually go into a Verizon store you are forced to wait just to talk to someone who doesn't even have the authority to make changes to your account, or assist you properly. To top it off their bills were long, and confusing, and at least back then their website was horrible for managing your bill online.
I hate the dropped calls on At&t, but other than that they've been nothing but good to me. I can actually get a real person on the phone within minutes for customer service, and they actually have authority to make changes to your account. There website is topnotch and lets you control a lot, and track your usage easily. I had one mistake/billing issue with At&t and with one 10 minute phone call they corrected the problem, removed the charges, and gave me extra rollover minutes, and bumped up my eligibility to upgrade to a 3GS and I didn't even have to talk to a manager.
As for data speeds, At&t is much faster than Verizon's network, and all major metropolitan cities have 3G. Since I probably spend more time using the data network on my iPhone now more so than making actual calls it's nice to have a speedy network, and good customer service.