They are indeed similar. I've had both, but I like DSL better. Cable connections are typically shared throughout a neighbourhood. That means that at 4PM, when all the kids come home from school and are downloading things, my speed slowed right down. Same thing goes for late nights on Friday and Saturday.
DSL on the other hand has been a consistent speed for me ever since I had it installed 2 years ago.
If you live in a condo or some sort of apartment building, I would definitely reccommend DSL over cable. If you're just in a house and getting cable would give you a price break or something like that, then you can probably go that route.
(If you're in Canada, don't sign up with Rogers)