One quality of an excellent friend is......

Calmness.
Well, anger leads to both emotional and physical suffering. Calmness gives a peace of mind. It has multiple advantages :
-severity towards violent behavior reduces
-one does not shifts to uncontrolled thoughts swiftly
-there is peace in the air, which gives the sense of hope
-lots of loud violent noise/argument leaves less space for innovative ideas to spring up for a problem
-calmness creates area for creative thinking
-calmness creates an opportunity for the introverts to speak up
-calmness brings all the people in discussion into a uniform state of silence
-calmness creates an environment of realisation and understanding
-calmness brings out hunger as priority over argument
-calmness also makes on aware of the surroundings
and so on...

This one quality of an excellent friend can be a blessing for life :)
Keep Smiling :)

good listener and always be there when u need them

Being a good listener

honesty & being supportive.

Lack of judgment; trying to help without looking down on you for needing help.

Being there for you

Who can listen to you unbiased

Validation and knowing that you will never be judged or belittled. :)

Talking out the issue as well as listening and being supportive like my girfriend, and my other pal, and also having like minds. :)

Being supportive through any situation.