Just an advice: don't own a dog if you live in a flat or don't have any garden.
Otherwise since I'm a child I always lived with dogs and they give you really postive vibration !
I know many people who keeps dog in a flat. I think this isn't a problem as long as you walk him regulary (at least 3 times a day) and if the dog doesn't have to be alone for the whole day or if the dog isn't to big for the flat.