Occasionally an Alsatian or similar breed.
But they would need to have a special function. Usually they’d serve as a military dog at an army base. I’d give it the genius, loyal and hunter trait, so it will be able to train and learn fast and find rare collectibles in the world in order to help my sims with whatever mission they’re on.
And...sometimes a kitten. Only because I like to watch it flop around the place. I never age them up. Silly little things.