Keeping in mind what others have said about how the networks are implemented, where are you and what are your likely disaster cases?
Here in central NC, Ice storms are the most frequent cause of no power and downed lines. Followed by tornadoes and hurricanes. Each of these can take you down for a long time. Or not. I work out of my home. My house is both on the 1st leg of the power system back to the substation and for some strange reason my transformer is tied directly to the "high" line, not the fused sub-feed line. And because of my neighborhood I've never gone more than 24 hours without power. Even when there are
100' trees lying on the lines on my side streets. Phone have rarely been down for more than a few hours, cable a day or two. Now 3 houses away on a side street they can be down a week.
Next on the list of issues is thunderstorms and lightning. While not as widespread, it can do enormous point damage. But if you have good backups and replacement gear is available at reasonable cost, maybe you don't worry much about this.
My point is you have to look at where you are located and what the likely sources of trouble will be and then decide first if you want to move and 2nd how much you to spend to avoid the troubles. Hurricanes, tornadoes, and lighting damage in Manhattan can be treated as 100 year events if that. For me they seem to average once a year.
Okay, and now for an answer from someone who works cable AND DSL BOTH.
It is a tremendous falsehood to say that cable doesn't have any resiliency. I know, because I've worked system projects from the maps that will tell you down to the foot where any given piece of equipment is. The maps are fairly LITTERED with power sites where power is handed off to the system from the power company and they DO have battery back-up AND the cable company DOES stock generators which are trotted out to the power sites whether ground/pedestal style or pole mounted if the outage will outlast the batteries.
This is ESPECIALLY true in areas with cable telephony. We've had every field tech above I/R (const., line, system engineer) tasked with delivering generators.
Cable goes back to nodes, and FIBER from there to a local hub and from that aggregation point to the head end and that's where you find the satellite dish farm. Sometimes they take their feed from fiber from some other head end even farther away. Depends on the operator and the services they've deployed. Here they are very reliable. No outage I've had has gone longer than a couple days EVER. I had SNET phone service out an entire week with the phone company unable to figure out where the break in the pair was in UNDER 5500 ft..
Phone service is SUPPOSEDLY a "five nines" service but is as with any human endeavor prone to error and breaks in the chain of service. Phone service CAN and HAS been out to customers for DAYS or even WEEKS with nothing better than buck-passing excuses. This DESPITE battery and generator coverage at the CO. I've seen SDSL and T1 lines go down and not come back for three weeks. SLAs are TARGETS, and NOT guarantees written in stone. Humans are required to honor them or give money back for services not rendered. They are NOT going to be there if someone screws up and people in telecom DO.
What needs to be asked is, "how important is this back-up line?" If very important, then what in the world is your MAIN line? I would predicate my choice of back-up on the main line to that site. For instance, if I had a T-1, I'd try to get the fastest thing I could without going over that speed and cost. After all, we're talking back-up. So either SDSL or cable. Too distant for straight copper, then definitely NOT IDSL or ISDN given cost versus speed. A cable modem business account can do as much as 1Mbps upstream depending on the provider. In pre-DOCSIS days, I had a modem doing 4Mbps upstream as a residential user. I get the much downstream regularly now.
If I had a DSL line already, I'd go with cable so as not to have the same point of failure, whether CO or RT. And vice versa. Right now, I'm looking at a pair of bonded SDSL lines to compliment cable.
If you've got line of sight and the bucks, you can get a VSAT link which then is only dependent on your remote site's power and not the cable or phone company.
At the bottom of speed would be something like Starband or DirecWay. But like VSAT these are dependent on your site's power and not subject to lines being disturbed.
There's no quick answer on DSL versus cable. But don't simply buy the line about DSL being superior to cable because the arguments aren't thorough. It's largely a draw technically and billing gives the edge to cable. But if you want to avoid physical layer delivery issues, satellite beats both. But it costs. So you've got a lot of weighing to do.
Any particular cable segment may serve upwards of a couple of thousand customers. To facilitate that service the cable co installs dozens of pole or ground mounted amplifiers and translators. Generally, the battery backups for these devices last no more than a few hours without power. Some last longer, some shorter as time passes and the batteries naturally loose capacity.
Thus, operation of your cable service is dependant on power and connectivity being supplied to ALL the cable co devices servicing your particular connection.
(In a nut shell, cable co connections are the worst of the worst, where Connectivity == function of power to all amps/translators+ long over head run of coax cable. )
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DSL is Better.. but still vulnerable, .it's reliability depends greatly on the type of phone lines used and how far they are run above ground. A falling tree knocking down and breaking phone cable makes for a long repair time. Underground cables at risk if their is extensive flooding.. (Enough to flood Junction or other boxes).
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DSL serviced by RT.. is a bit better than cable, usually only one battery to go down.. Overhead wiring at risk, Pad mounted boxes subject to flooding.
A friend who had phone service via SLIC s lost dial tone, after 6 hours. Phone line intact, hurricane & tropical storm conditions lasted for several days, during which no repairs were attempted. After a couple of days the phone company rolled out a diesel genny to power the SLICK and restore phone service.
Note: I don't recall the phone co going out their way to power any stand alone RT's(DSL) boxes.
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DSL serviced by CO is better yet (Battery + full time genny),. overhead wiring still at risk, Junction boxes still at risk of flooding.
I had DSL to CO and /internet connectivity through out Hurricane Frances despite having lost neighborhood power for over 4 days.
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Lastly, even if you have local connectivity.. how about your ISP? If their routers are not up, your data is going nowhere fast. What's their connectivity look like, do they have genny's?
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