I've finally chosen a new phone. I picked the T-Mobile myTouch, an Android device, over Apple's iPhone.
The actual device was less a factor for me than cost of the plan and quality of the network. The iPhone is clearly a more advanced creature (although the myTouch is good enough for me). T-Mobile's data plan is cheaper. In fact, thanks to a customer loyalty program (I've been withT-Mobile for a few years) I was able to get unlimited minutes, unlimited data, and 400 text messages per month for about $75.
The T-Mobile network, while not always perfect, has been generally reliable. All the stories about dropped calls and 3G outages on the iPhone with AT&T scared me away.