The coverage issue varies a lot depending upon where you are. In some areas, Verizon has better coverage, others at&t. I happen to have T-Mobile and, overall, the coverage seems fine for my purposes. Actually, in my own house the signal is only one or two bars, but my phone has WiFi, so that kicks in anyway. From the coverage standpoint, its probably best to check with others that have a carrier in the places you're most likely to use the phone and see what kind of signal they get.
Of course, if you're going with the iPhone, at&t is it for now. I hear that Apple will be going to other carriers, but I don't know of a date. I had thought the original agreement between at&t and Apple for the 1st gen iPhone was that at&t would have exclusivity for 5 years. Perhaps that's been modified, but we're also well into that 5 years. If you strongly feel Verizon is the carrier for you, you may just want to stick with your existing phone/carrier until Verizon picks up the device, rather than signing away 2 years with at&t.
Personally, I'm happy with the BlackBerry. I don't worry much about the radiation issue since my conversations tend to be fairly short. I use it more for data anyway and many of my conversations are in the car, where I have a Bluetooth connection (not the ear thing; it goes thru the car stereo), so I'm not holding it up to my ear anyway. Unless you're holding the device to your ear for frequent and long periods of time, radiation shouldn't be an issue. I'd base my device choice on features, carrier and price, not radiation.