I notice my three will eat almost every different variety of Royal Canin dry, though some are preferred to others (though Tiffany won't eat the Light, on the grounds of being insulted
)
they are much less likely to eat any other manufacturer's dry food though
is this probably because Royal Canin uses some flavouring which they look for?
I think this could be important, as it might mean it is better to start off with a company which makes prescription diets, as they are more likely to be accepted if necessary further down the line