1) Comcast cable. ...
Their phone service almost certainly isn't Vonage-style parasitic VoIP but rather packetcable which uses IP signalling over dedicated bandwidth.
2) Sprint, which is the local LEC and DSL. ...
> Does anyone have an opinion on which will be more relieable and more
> responsive to problems?
Sprint, formerly United Telephone, has a pretty decent reputation as an ILEC. I expect either would be fine, but if the power fails, your Comcast phone service will depend on batteries in the box they install on your house and in various cable boxes on the pole, while ILEC service is usually powered from the CO.
R's,
John