OP, from experience (and reading the replies here) it seems the best thing is to ask neighbors/visitors to your home what they have and how the signal is. We originally got Verizon because the salesperson showed us on his map that we are in a great coverage area (in a laaaaaarge suburb, not rural). When I took that phone back and was released from my contract, after talking to several RUDE csr's, one finally told me that I live in a "known trouble area" for reception.
It MAY have changed since then, but I had 30 days to try a new phone/company. So just don't mail in a rebate on your new phone till you know how it will work out for you! I think I was out only the $30 (or so) activation fee. I fought that, too, since the verizon guy was so adamant that we had the strongest signal possible in our neighborhood, but at least I got out of that contract.
I tried Sprint next (signal iffy). Then went to Cingular, which turned into AT&T, and stuck with it.