Comcast cable internet is rarely the only option for internet in any given community. There is almost always an option to get a DSL product from the phone company. Which means you basically have to have a landline. So you pay somewhere close to the same amount of money for much slower internet.
If I was in a community where it was DSL on AT+T copper or comcast I'd probably go with comcast.
In my experience, I've found that what's available varies greatly, even within the same metro area or even city. I used to live in a Northwest Chicago suburb: there were several cable (tv/net) providers, but I lived in a multi-unit building, and Comcast actually owned the building's infrastructure, so they were literally the only option.
I now live in a house in a sparsely-populated part of the City of Chicago, and AT&T and Comcast are the only two options, even though other areas of the city have more options.
I had Comcast cable-based high-speed internet (HSI). I started in on a promo rate that was about $50/month (IIRC) for HSI and basic cable (very basic, effectively local broadcast plus religious, public access and shopping channels). I didn't want the cable, but the promo HSI rate only applied if I got some TV service, so it was actually cheaper to get HSI plus TV rather than HSI alone.
Eventually the promo ran out, and Comcast wouldn't negotiate. I tried calling several times, going straight to the "Cancellations Department", etc etc, and couldn't get them to extend the promo rate. The HSI+TV cost went up to $75/month, and HSI alone was $60/month. To Comcast's credit, the HSI service was generally fast and reliable. But I thought it was too much.
At the same time, AT&T happened to be offering their DSL service for $20/month for the fastest "Elite" tier (6 MB/s). Prices go down from there. I already have a land-line due to having a security system, but I read the promotional material very closely, at it sounded like you could get the same DSL deal without an actual phone line. I was hesitant, but found the DSLReports Forums to be very helpful. One, I was able to ping other forum users to see if there was anyone in my neighborhood with the service (an informal survey of sorts). Two, they have dedicated, private tech support forums where you can actually talk directly to a tech person about the service. In other words, at the cost of waiting a day or two for a response, you actually get a useful answer from someone who knows something, rather than taking your chances with the yahoos at the 1-800 number.
That $20/month is guaranteed for a year, but without any contract (cancel any time), and no setup or equipment fees. I was quite skeptical, but we've had the service for over two months now, and I haven't had any problems. It is slower than Comcast's HSI, but fast enough for streaming HD Netflix, which is our highest requirement.
By the way, my landline is about $16/month, bringing my total monthly outlay to AT&T to $36/month, still cheaper than Comcast. We use cellphones for everything, but need a landline for the security system. If you live in Illinois and have a similar requirement (basic land line service), check out the Citizen's Utility Board. They have negotiated an AT&T plan called "Consumer's Choice Basic", which is as cheap as possible for AT&T. When I signed up for this, it wasn't available online, and I had to call their 1-800 number to get it... and even then, they are shady and try to add services if you don't pay close attention to your order.