I had Alltel, but no signal at my house (CDMA); but my brother was on Suncom and did (GSM). So, I ended up switching to Cingular, which became AT&T. Most places, I'll concur that Verizon has broader coverage, but, if where I need it, Verizon doesn't and AT&T does, well, it's AT&T for me.
So, yes, in town, AT&T is fine, but not as good as Verizon off and about out of town. But off in the coalfields, neither is great. When Verizon bought Alltel, here, they had to spin off this RSA to AT&T, so AT&T has been converting their towers here locally to GSM: my coverage is vastly improving.
I hate Apple. Was an Apple guy in 70's, early 80's, but switched to Windows when the II-line was killed off for the Macs. I've had Walkmans and Zunes for mp3 players instead of iPods. But, I really like my iPhone 4. There are some things I don't like, such as not being able to group photos into folders on the phone (I can pull them off to a PC, group them, then load them back, but can't manage it while on the phone). But overall, it's a competent piece of hardware that simply works well.
My dad and brother have Droid X's, and the fella I carpool with has a Droid Incredible, all on Verizon. Theirs are competent phones, but if all else was equal, I'd grab the iPhone before the Droids. I wouldn't have changed carriers to get it, but for my particular location, AT&T works better.
Before today, an iPhone didn't make sense if you needed to be on Verizon. But now, you simply have a choice.
FWIW....