The best option for lines to and from your ISP depends on what your requirements are.
The cheapest is asymmetric digital subscriber line, or ADSL. This has good download capacity, but very small upstream capacity. It is most often used for residential purpose, for users who like to browse the internet but don’t need to send much data.
The next option is symmetric digital subscriber line, or SDSL. In this option, the upload and download capacity are the same. The maximum download capacity is not as great as the best ADSL, but it has significantly better upload. This is more expensive than ADSL, but is more suitable for small to medium-sized businesses.
The final option is leased lines. They are more expensive, some very much so, but sometimes the cost-benefit analysis shows that this is the best option.
Like SDSL, leased lines are symmetric (ie same upload and download capacity). A leased line is a fixed line connecting two locations, therefore it doesn’t have a telephone number as each end of the line is permanently connected. It carries telephone, data or internet services. Leased lines are known as ‘Private Circuit’ or ‘Data Line’ in the UK. An example is BT’s kilostream or megastream.
There is plenty of competition in the market, with many leased line, ADSL and SDSL providers.