You're choice for a broadband ISP is usually restricted by where you live.

1) Cable-modem:
I'd have to say that after using DSL for many years (ADSL, SDSL...etc...) cable-modem appears to be a lot faster.
Although, I do notice an occasional slowdown, cable-modem appears faster then DSL (especially compared to the basic DSL offers you usually see in the $30/month range).

For cable-modem, today you will have mostly one choice: You local cable TV provider.
So check their web site to review their offer (contracts?, services ?, price ?).

In my market (Colorado) Comcast is the main provider. I've been using their "deluxe" cable offer and have been pretty happy with it. Click the following link for a Comcast special offer:

Additional high speed internet services cable TV providers:

Charter Communications:

2) DSL:
Today DSL is offered by all regional phone companies, a few specialized DSL entities, and some larger Dial-up companies that entered the DSL market. You will usually have a choice up to 5 providers.

Here are some of the major DSL offers:

Verizon DSL:

 

BellSouth FastAccess DSL:

 

AT&T High Speed Internet (Yahoo!):

 

3) Fiber Optics:
Availability of this service is still very limited in the US.

Verizon FiOS:

 

Remember to ask friends or neighbors around you. Usually this is a good way to know which offers are the best in your area.