I have a female "Taco Bell" look alike chihuahua that's now 12 years old. I have a rottweiler puppy who's 6 months old. I also have 2 cats whom both dogs love. My chihuahua, Minnie and my rott, Zeus play together fine. I'd have to say though that Minnie definately is the boss of the house. I can't say that I have a favorite breed. I can say that a dog is only as good as its teacher. Dogs aren't born mean they are only products of their environment, so of course if they are taught to be mean and aren't properly socialized they will be mean. Taking care of any animal is a big responsibiliy and should be given lots of thought.