I've had both cable and dsl.
While dsl is slightly more reliable it's not as fast as cable here in metro atlanta. Cable boasts 3000 kbps while dsl is still only about 1200 kbps.
30% downtime is high. Sounds like a local problem that maybe the cable guy can fix.
At one location the cable I used was down frequently. It turned out the problem was an amplifier the comcast installed to improve tv reception. This overloaded the modem however.
At my current location (about 7 months) the cable is more reliable than the dsl installation I had the year before.
dsl is sometimes tricky because it uses extra bandwidth on the twisted copper lines that the phone company owning the lines can lease to another company. However my earthlink dsl got blown out of the water when we inadvertently switched to another local phone provider which garnered the leased bandwidth from the real phone company.
If the cable guy can't give you 99% up time than you may want to call the local phone company (not a 3rd part dsl provider).
You can review the reliability of different providers in your area at
www.dslreports.com