I fear my earlier answer may have been a little harsh - hence the deletion ;-(
I prefer dogs because they are not selfish.
A dog seeks to please it's owner, a cat seeks to please itself.
A dog will come when called, a cat will look at your disdainfully and stay where it is.
A dog will protect you, a cat will click into self preservation mode (actually it never leaves that mode).
A dog can be enjoyed as a social pet on family hikes, a cat is antisocial
A dog looks nice, a cat doesn't.