iPhone switchers?

Has anyone (especially in Boston) switched from AT&T to one of the other carriers who now offer iPhones? Have you found it to be, in fact, any of better, faster, and/or cheaper? I've been with CellularOne—>ATTWS—>Cingular—>A$&T for something like 12 or 14 years now.   I've stuck with them largely on the better the devil you know theory: They've always sucked, but as best I could tell, they sucked no more than anyone else, and possibly less. But my contract expires in a few weeks, and my iPhone 4 is still going strong. So it seems likely I'll be able to continue with my pattern so far of only buying an iPhone every second generation (i.e., wait for the iPhone 5 to upgrade). Which should also mean I have time to actually compare carriers this time around.

So: anyone had the experience of switching? What do you think?