Lion, I have a cable modem and it is very fast indeed. I can download a 10MB program in a few secs. Sometimes. It depends on the site. As for browsing, it is considerably faster than a phone modem. You also have the added benefit of freeing up your phone if you only have the one line.
There’s a downside. (Always is). Cable can only carry so much information, and as more people sign on, the bandwidth has to be shared, which tends to slow things down. But it will always be faster than what you have now.
You also have to be certain that you get a compatible modem for the cable you have. Your cable company can help you with that. They may even sell them. They are pricey, though.
If you can rent a cable modem, that might be a good idea. Then you can make a more informed decision on whether to buy.
Personally, I would not go back to a phone modem now. I’ve been spoiled.
This space for rent.