If you think your living situation might change, which would make you unable to care for a dog for its entire lifetime, you should consider not getting one. It is very difficult and sometimes impossible to find a home for an adult dog if you had to give it up for some reason. You must consider where the dog will be kept. If you have a large house with a large yard, any type of dog would probably be good. However, if you have a apartment with no yard, you need a less active dog that doesn't require as much exercise as a large, active dog.
Dogs are very social pets.
They will require your time to play, groom, exercise, and train. If you are not at home most of the day, and the dog will be left alone, consider another type of pet. Dogs require yearly shots, grooming, toys, and food. Puppies will cost more at the vet initially. Some types of dogs require more grooming than others and are more prone to have health problems, which might be costly.