TC cable is fast, and generally very reliable reliable, but it stops working in a power cut. I'm told there are pole mounted repeaters, and they can't put battery backup into them. That's rarely a problem though, cable internet rarely goes down.
Oh that's interesting. Telstra HFC in Australia is battery backed up. I assumed the pole mounted repeaters were passive, but I clearly I thought wrong.
To the OP though... it's impossible to say what speed your DSL will run at. Generally if you're within 2km to the cabinet/exchange you'll get at least 10mbit - but there's just too many factors to take into account. The only way to reliably know what speed you will get is to take the plunge.
I only learned that in the power cut a week or so ago, there's a thread about it here.