I gather the main difference between cable and DSL is that with DSL you have a line to yourself, whereas with cable, you share a connection with other subscribers. If you're old enough to remember when phone lines were party lines, that's a parallel of sorts.
Two possible drawbacks of that scenario are: variable speed, depending on how many other subscribers there are and how many of them are on line at the same time; and the security issues resulting from the fact that you are essentially sharing a network with all those people.
Computer security being what it is, there are ways of protecting yourself, of course, and if you are using the connection at times other than heavy traffic times, you won't have much impact from sharing the connection. But those are the issues that keep us with DSL, and we've found the speed to be more than acceptable.