Yes, in general a Dog has lot of Good Qualities, as far as human values are concerned.
But some dogs are quarrelsome, but these are the ones who are fed on bad things and having bad association, just like in case of humans.
I have seen some Dogs are devoted to some temples.
Also i have a personal experience. There was one dog in the vicinity of my work place. Now i used to give him biscuits some times, when i used to come across him. Then there was a change in the location of my workplace & for about 10 months or so, i had no association of that dog & i forgot about him. After coming back, i saw that the same dog was following me, although i had forgotten completely about him. So Dogs have a very sharp memory...All is God's power.
Om Sai Ram