Your dogs temperament should match yours. Do not choose a breed that is highly energetic if you are a couch potato. On the other hand, if you want a dog that will follow you everywhere around the house and who is always ready for a game of fetch or tug of war then you should consider a dog that is highly active and always has a lot of energy, instead of one of the lethargic breeds.
Keep in mind that large dogs are more expensive to keep. They eat more food, which costs you more money. Tick and flea preventives cost more for large dogs, as do other mediations.
All dogs should get as much exercise as possible. A daily walk is sufficient for most breeds. But most small dog breeds, for example Toy dogs such as Pugs, Maltese or Yorkshire Terriers, will get the majority of their required exercise needs just be walking, running and playing around indoors.
If you do not like loose dog hair and do not want to be vacuuming the house every day, then do not buy a high shedding breed. If you own a high shedding dog you will find hair everywhere! Including on your clothes, on your furniture, in your bed, and even in your food. Additionally dogs that have a high shedding rate need to be brushed more often to brush out the dead hair.