I would have to say that temperment is the number 1 priority when searching out a companion dog (or a working dog for that matter). I had a few dogs with "issues" who never made great companions ... some can adapt through rehabilitation programs, but they never quite get "there". My ideal dog is my Jack Russell - highly intelligent, independent thinker, is happy to be with you doing nothing, but is "ready" at the drop of a hat. Play and food motivation are important to me, as well as a level of prey drive. I like some protectiveness, and I don't mind some mild dog aggression. I like the dominant dogs, and I do have a preference for females. I also have a preference for small dogs. I do not like "clingy" dogs and I don't need a dog in my face 24 hours a day. I also do not like hyperactiveness or highstrung dogs - both of which I consider to be temperment or training issues. I guess the "terrier" temperment is what I appriciate most - highly intelligent, bold, fearless, strong, tough, independant, loyal, loving and scrappy.