The main differences are:

xDSL- dedicated line.
aDSL is usually used by residential areas. Faster download then upload. ex. 768/128
sDSL is usually used by small/large businesses. transfer rates are about the same, up and down. more expensive.

Cable is pretty fast depending on what they allocate to your area and how many people are using it.

I've seen some people get 1mb down 256k up or 2mb down 256k up. You share all this bandwidth with everyone on your segment. So, if all the neighborhood punks are using filesharing 24/7, then your speeds can reflect those of dialup.

The price depends on the competitors in the area and the cost to them, providing you the service.

In my area, cable with speeds of approx 1mb/256k is ~$50/month. DSL with speeds of 768k/128k is ~$20/month. I am just south of Philly... with many major cities around... so the cost of them providing the service to me isn't that much... they have all the major businesses in/around me paying the majority of their costs...

I prefer DSL because it is dedicated. I don't have to worry about what time the my bandwidth will be available to me again, so I can download the latest linux distro.