Unlimited Vs Limited, DSL VS Cable... which modem? all those questions is hard to answer for someone who all he needs at how is a good internet service :)
What You Need to Know About Different Types of Internet Service
First, it's worthwhile to know the differences between the types of internet service available. "Broadband" is an umbrella term that covers all of the always-on types of internet connections: cable, satellite, DSL, and fiber optic service These are the high-speed internet services that keep you constantly connected. The other option is dial-up.
here is more details to understand the difference
DSL or Cable
If you regularly use the internet, you will probably want a DSL or cable connection. Cable can be faster than DSL, but most people can find what they need from either one of these services. Also, for those who want a reliable wireless connection, you can connect to DSL or cable internet wirelessly with a wireless router.
If you regularly use the internet, but live in an area where DSL or cable connections are not available, a satellite connection may be your best option. Satellite connections are wireless and much faster than dial-up, but they are limited in their ability to connect to streaming content, can be affected by the weather, and their price is comparable to DSL or cable connections.
head to http://dslreports.com/search and enter your zip code. you can compere different service providers there. DSL Reports breaks down broadband options near you by category and provides user ratings across factors such as connection reliability and value for the money.
The comparison sites are a good starting point to quickly identify which ISPs have the best combination of speeds and price. price is important but I would aim for the speed first and the availability You'll also need to visit the individual ISPs' websites to get the fine details on their packages so you can make a thorough comparison for yourself, based on your needs. In particular, pay attention to:
Download and Upload Speeds: We all want fastest internet at the price we're willing to pay. Make sure when you're comparing services, you do so on an apples-to-apples basis, comparing the most similar plans based on both download and upload speeds. To find the ISPs with the fastest upload and download speeds actually tested by users worldwide, visit Speedtest.net's Net Index. Click on the map to drill down to your area and scroll down to the ranking of ISPs by speed index (available for download and upload speeds, as well as network quality).
Cost and Contract: Some services require you to rent the modem or buy it yourself; others provide it for you. Some offer free installation while others charge you for that service call. Most discount your internet service if you package it with television and/or phone service (but often only for a few months, so be sure to compare costs including after the bundle expires as well). And you might be able to avoid a multi-year contract with some—for a higher price, of course. These are the details you'll need to consider when comparing services by price.
Terms of Service: Similarly, make sure you know what the service's limitations are. There may be data caps, for example, limiting the amount of data you can use per month, or restrictions on the kinds of activities you're allowed to do, such as running a web or file server.
Add-ons and special features: Many ISPs throw in extras just to make it seem like you're getting a great value. Things like anti-virus program subscriptions, an ISP-branded email address, and personal webpages are just that—extras that you likely don't need. One pretty cool add-on you might find, though, is free Wi-Fi hotspot access. For example, if you're a Cablevision customer anywhere near one of its public Wi-Fi towers (whether you're in a building like a coffeeshop or outside in the park), you can hop on to it. That might sway you if you frequently use your laptop on the go.
Reliability: Of course, none of these features matter if you can't use the service when you need to. DSL Reports shows reviews from your neighbors, which is a great start. As mentioned above, you can also use the Net Index from Speedtest.net to get a ranking of real-world ISP quality tests.
Customer support: If you experience outages or other problems with the internet (as will happen), how easy is it to get support? Does the provider offer phone, email, or chat customer support? How painful or painless is the installation process? JD Power's Residenial Internet Service Provider Ratings measures ISP customers' satisfaction across several factors, including performance and customer service.