DSL (Digital Subscriber Line) refers to internet service provided over the telephone network. Although DSL lines are not shared, its speeds are historically the slowest of available internet services, and usually advertised at speeds of up to 15Mbps.
DSL performance is also distance sensitive: the longer the phone line between your home and the phone hub, the worse your internet connection performs. DSL is further affected by the quality of the copper wiring in your phone line.
Cable internet uses the coaxial cable that connects to your television set. Although cable technology can run much faster than DSL, its performance is dependent on how the cable line is shared between you and your neighbours. If many people in your area go online at once, cable speeds for you (and everyone else) will suffer.
Fibre broadband, using fibre optics, is the best technology at present for high-speed internet access. It can transfer data at least 10 times faster than copper lines, with typical advertised speeds starting at 100Mbps.
Besides putting out superior performance, because fibre optic cables use glass as a conductor and transmit pulses of light instead of electricity, fibre broadband is immune to all kinds of outside electromagnetic interference such as lightning or high-voltage power lines.
Simply put, fibre broadband is much faster and more reliable.