I have a simple definition of what makes a nice dog - one that doesn't scare mine. I have to admit she is a wuss. Now I wouldn't care but when she is frightened, someone gets hurt and that is usually me. She gets scared and jumps on me and bruises usually appear, on me.
This was a nice dog - they checked out each other's butt, ran around a bit and separated. No bruises - a good day, a nice dog.