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.
-Wayd Wolf