dogs can't process theobromine in the cocoa, starting ingredient of chocolate. See wiki for more information. Higher the cocoa content of chocolate higher the content of theobromine.

Sooo... Dark chocolate 82% pure cocoa would have more theobromine than a 60% dark chocolate in turn has more theobromine than a milk chocolate. Most white chocolate really isn't chocolate so doesn't count.

Regardless, its not good idea to feed your dogs chocolate, raisins, grape... And dogs being an omnivore like human have sweet tooth. Cats are strict carnivore and do not have the sweet receptor, no sweet tooth. Cats are less likely to indulge in chocolate.

you should not feed your cat any chocolate, raisin, or grape either.