As an ADSL user (and with friends who have cable) what I can say is:
- Cable is directly affected by the number of users. DSL is not. If you're in an area with limited cable use, you should have speed.
- DSL is affected by your distance from the main phone switch so speed will vary depending on that. My DSL account will allow for up to 3 megabit access although where I live limits me to approximately 2.3 - still not bad but only made possible since Bell starting upgrading its lines and installing repeaters. When I lived about 1 km closer to the switch, my speed was slightly better.
Where my mother lives, farther from the switch, her DSL access drops to less than 1 megabit.
Essentially, both types of connections can have speed issues - just originating from different sources.
I've never used cable so I can't speak of its consistency but DSL have worked well for me and my mother. The biggest issue with it (again) is distance. Before switching, try to find out more about the quality in your area from those who use it.
I know this is probably a silly question, but is
there anything I can do to increase my internet
speed? I currently have a cable connection, which is
supposed to be fast, but it is so slow. I've been
told that when there are too many users sharing a
cable line that the speed decreases. So sometimes
you're better off with a DSL connection, which is
more consistent. Is this true?