Most internet service providers use ADSL, as it is available on a large scale. In order to use ADSL, you only need an ADSL modem, connected to a regular phone line. A standard AT&T DSL connection costs just around $20 per month, for a 6 Mbps/768 Kbps connection.
VDSL is one of the new technologies, but is not easily available everywhere. The speed basically depends on the proximity between you and the carrier’s location. Speed is certainly a very important factor, and is the obvious difference between the two as you can get download speeds up to 50 Mbps when using VDSL.
However, the problem with VDSL is that the speed is limited to local loops such as your neighbourhood. The speed will continue to decrease as you move away from your service provider's main office. A fibre optic cable is required to route the data, and while most telephone companies are upgrading their phone lines, it will still take some years before countries manage to lay down fibre optics everywhere.
With the help of modern advancements, this problem can be resolved by routing fibre optic cable to a main location from where the VDSL signal can then be distributed to the subscribers. Cost price plays a major role in the decision making process when getting an internet connection. You need to know that while VDSL is a high speed connection, it comes with a high price. It is being offered by AT&T for $100 a month as of October 2010, which does not include the equipment fees.