They are are the best breed in the world. Bar none. PROVIDED you get one from a reputable breeder, that has had all the necessary health checks done, see the parents/family, visit several times to meet the puppy and the breeder's other dogs, take time to train and socialise it,
and have just a teensy bit of good luck thrown in as well.
A male Shepherd may try to dominate the other dogs, so you might consider a female if your other two are males. Also vice versa! The cats will be no problem provided you get a puppy and it is brought up with them. The planned family will have the best friend/protector in the world. You will have the most loyal loving companion who will lay down his life for you without question. Please do it justice by taking it everywhere with you, and not just have it as a 'yard dog' or lap dog. They need to have a job to do to keep them occupied, so maybe try obedience or agility or at least regular exercise and training sessions. Now I'm getting broody!