Dive Computers tend to come in two different forms, you can get the ones which attach to your wrist like a watch and the ones which attach to (Or replace!) your pressure gauge.
Wrist Mounted computers have the advantage of being on your wrist (of course!) which makes it very convenient to check all your dive information.
Some are have also been designed with more than functionality in mind; Sleek, stylish units which could be just as easily worn on a social occasion or a week long dive trip!
Console computers are larger and bulkier than the wrist unit but do have the advantage of being attached to your regulators, so possibly a little harder to forget! Some of them offer air integration and can completely replace your analog gauge.
A common disadvantage of console units is the bulk and how often they can be seen trailing beneath a diver presenting a entanglement hazard and damaging to the environment as it drags across the reefs.