reply to jimbecher
Here is how I think of it, when answering the reliability question...
T1 or T3 line is "powered" by the phone company, the phone company is very good about keeping all there equipment powered even when there is a disaster or major power outage because all their equipment is actually run by battery banks. These banks can run the equipment for 8+ hours, and are kept charging when line power is available. Because a T1 or T3 may carry voice traffic, such as 911 calls, up-time is important. Even if there are ground vaults or other devices that require power between the phone company's central office (datacenter) and your office, these are all treated with the same battery banks, and pre-terminated trailer generator connections. Phone tech's will tell you that T1 and other Hi-capacity lines usually get fixed first, POTS (or a single analog line with 1 number) will get fixed last. In many cases (but not all) you can consider a line from the phone company a "home run" to your location - as in, it's dedicated to you (your business) all the way from them (the phone company central office).
The cable company however (like Comcast) requires many, many, more powered amps and splitters along the coax line. Sometimes these are aerial (on the line up near the power pole) and sometimes these are on the ground, either way they require power usually taken from the nearest power pole, and only sometimes do these get a UPS system (usually a cabinet that says Alpha on it, at least in IL) and this UPS is only good for about 6 hours (at least in my area, IL) When a cabinet is run out of battery, that's it, there is no pre-terminated generator connection, nor do they think it important to bring one. On the rare case that they do, I've seen them take your standard construction site little gas generator, chain it to the power pole, and hard-wire it into the Alpha cabinet, leaving the front panel off so the cord will run in. :-/ Obviously if a large area is without power, they can't afford or keep doing this to the hundreds of Alpha cabinets in the area - they just "give up" and wait for power to be restored. Beyond the power issue is the "shared" issue, the coax line is shared by all customers off the local cable plant, when one splitter needs to be replaced, or put in-line, they don't think twice about cutting everyone's service out to do it. Similarly when one amp needs replacing, it cuts off everything else further down the line.
Supposedly, "Business class" cable modem service is supposed to get better throughput than Residential, and in most areas it's true, but you have to remember both are part of the same, single, coax cable run through your community, so one cannot really be considered more reliable, and any SLA is really only intended to make you "feel good" or give you better credits for downtime, there is nothing physically different about the service. The exception is when Comcast can offer you a fiber line, or there equivalent of Metro Ethernet, which is not coming into your building over coax - this is much pricier.
The actual data part, in terms of routing is pretty similar between the two - in both cases the routing and Internet redundancy is done back and the central office, not out at the street level.
Regardless of your connection type, within your company your should have the modem/router/CPE connected to your own, long lasting, UPS.
You need to decide how important your phone/data service is, and have a backup plan (call forwarding) if it goes down.
As an example, when major storms came through this July in IL, and many were without power for days...
- My customers on cable modem did OK for anywhere from 4 to 7 hours after the loss of power (Alpha boxes were still powering the line, but were then depleted) This is about the same as why traffic lights blink red for awhile after the power outage, but then eventually go dark)
- My customers on T1 or T3 lines never lost service however
...if your not concerned about such extreme cases, maybe paying significantly less for monthly service is acceptable - more often then not that's what small businesses choose.