Connection Speed
Choosing the right speed for your connection can be quite difficult. Generally aim on the lower side, that way if you need more speed it is easy to see that and you can upgrade easily. If you choose a higher speed that you find you don't need, broadband suppliers are more reluctant to downgrade your service.
If you have a single PC then a 512k service is likely to be adequate in all but the most extreme requirements. If you are requiring adding more PCs to the same broadband connection then a higher speed might be required. Some suppliers force you to take a higher speed if you plan to connect more than one PC.
If you plan to make use of interactive services such as video conferencing, online gaming then there is also a case for a higher speed service.