The answer to your question will vary *widely* depending on the local deals, how congested the network in your region is, etc.
In general, cable modems will usually be cheaper for more bandwidth. However (and I believe that SF/Silicon Valley suffer from this problem), the aggregate network bandwidth of the entire cable-modem segment is shared between all users. That means that if you have 1000 people on the "segment" you are on and everyone is downloading simultaneously, you're all going to split the available bandwidth and thus be pretty slow. However, in areas where the cable companies were able to plan the rollout better (and keep the number of homes on each segment under control), this is generally not a problem. For example, I routinely peg my 3.0mbps (about 380KB/sec) cable connection.
DSL, on the other hand, is delivered via your telephone line and is generally more available to more people. However, the price you pay for DSL, while somewhat cheaper, usually buys you *much* less bandwidth. For example, in my area, my 3.0mbps cable modem is $46/month whereas DSL (IF I could get it) is only 768kbps for around that same price. However, if you live in a poorly designed cable-modem area as described above, DSL will probably get you more reliable speeds.
Both DSL and cable providers frequently run agressive pricing deals. My buddy in Texas got SBC (IIRC) DSL with a 3.0mbps downstream/768kbps upstream on a "special deal" for a year at around $50/month (normally closer to $100). He's obviously going to have to figure-out what to do at the end of the year when deal runs-out, but I would not be surprised if they renewed him just to keep the money coming-in. Here in my area, ComCrap is offering a special (for new customers only
) where the first 6 months are half price (so around what you're paying for AOL now). Thus, you'll just have to talk with people in your area and find-out how pleased they are with whatever service and make your decision based upon the specials, performance, etc.
BTW, an excellent forum to go read what people think of various ISPs is:
http://www.dslreports.com/
Hope that helps,
Mike