It very much depends on the area, not just the local carrier, but the part of town. You won't really know until you have been there a while, although the opinions of neighbors should be useful. A rule of thumb is telephone networks have more built in reliability, but the service is a guess.
If you go with a cable modem, there are other voip carriers that you can use instead of the cable company, that are probably less expensive. I have had good luck with both Packet 8 and Earthlink. The former uses less bandwidth, the latter has better audio quality. In both there is a little noticeable delay, but not bad.
If you go with DSL, the phone company will probably only provide it if you buy telephony from them. Also, DSL tends to have somewhat less bandwidth than a cable modem.