Simply fantastic article in today's New York Times about how AT&T's wireless service is actually BETTER than Verizon, and why consumer perception is the opposite.
You may know that because of the iPhone, and more importantly, the iPhone 3G that debuted in 2008, data usage on AT&T's network jumped 4000%! No one could have predicted that. And iPhone users still use way more data than any other smartphone on any other carrier combined.
Take that 4000% increase and stick it on Verizon's dated CDMA network - how do you think it would fare? (GSM, choice of AT&T and T-Mobile, is the global standard. Verizon is reportedly considering LTE 4G technology, which
is explained here.) The Verizon zombies would have you believe the network can handle it - but you don't know until it actually happens.
I can only go on practical experience. I haven't suffered too many dropped calls, but I tend to lose 3G data and texting capabilities when I'm in places with a ton of people (like say, Gillette Stadium or the Garden). If that Times article is right, those are problems due to Apple design, not AT&T service. Mrs. SCZA on the other hand, seems to have acceptable data service, but complains of a ton of dropped calls on her Blackberry Bold 9000 (my co-workers, who all have Blackberry Curves on AT&T, have the same complaints). That leads me to believe it's a Blackberry thing, rather than AT&T. I'm contemplating getting her the new Bold 9700 that just came out and seeing if there's a significant difference.
Either way, I think you can safely say the cell phone service competition is a myth. Everyone is going to get a different result with different carriers depending on where they live and work. I had Sprint for years and never had a complaint about the service (I swear its 3G on a Blackberry was faster than on AT&T) and the same plan for me and the Mrs. cost 80 DOLLARS LESS than it does on AT&T (and Verizon, I priced it out). But I've also talked to people who have had miserable experiences with Sprint too.
Now T-Mobile is offering family talk/data plans that undercut even Sprint. And there are a host of startups, like Metro PCS (who buy space on Sprint and Verizon's CDMA towers), that will get you unlimited plans for as little as 45 bucks. So the best advice is probably to find out which carriers offer the best service in your area and then shop for the best deal. Don't let the reputations of one or all sway because the difference in service is not that great to justify the difference in price (unless you really, really, really need an iPhone).