Nintendogs is FAR superior to the dogz/catz games
first off the graphics are much better, and the view of the dog is more on the level of the pet as if you were sitting on the floor with them, as opposed to the top down SIMS type of view for dogz/catz. You can play with the dog in Nin-Dogs much more realistically (pet, throw things, etc.). I don't really have the list of specs to give you a side by side comparison, but having seen both games played, that is the biggest and most significant difference, which, IMO, makes them completely different games (Nin-Dogs being better).
I was kinda surprised that Ubisoft put their name on the dogz/catz games, they really are sub-par in my experience.