I vote Nintendogs.
Nintendogs
Good things
> The breeds are realistic
> The graphics are clear
> The settings are realistic
> You can interact with other Nintendogs users
> It's enjoyable for both boys and girls
> You can use sound and the touch pad to really interact with your dog
> If you neglect your dog, you don't lose it
> You can train your dog tricks
> You can enter your dog in competitions
> It's like owning a real dog, for the people who can't have a real dog for whatever reason - the dogs act the way a real dog would
> Children and adults can play it
> The cheats on it aren't too unrealistic (eg. dogs turning purple)
Bad things
> After a while, the game becomes repetitive and boring
> It could come out in another version with more breeds - the current breeds are "boring" to some
> Dogs' names can only have so many letters
> The Nintendo DS can be bulky to carry around
> Playing in public may cause unwanted stares
> The chocolate Labrador has a black nose, which is impossible. Liver, or chocolate is when a dog can't produce eumelanin (black pigment) so the dog is turned from black to brown with a brown nose and yellow or light brown eyes.
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I can't really comment on Dogz as I've never played it before

I have, however, seen the graphics - they're much too pixel-y in my opinion. Too blocky and cheap-looking.