Which term is best used to describe a person who is ill-tempered and quarrelsome?

The term that best describes a person who is ill-tempered and quarrelsome is "cantankerous." This word specifically refers to someone who is difficult to deal with, irritable, and often prone to arguing or being disagreeable. It captures the essence of a person who is not only uncooperative but also frequently in conflict with others, which aligns perfectly with the description of an ill-tempered disposition.

Other terms like "benign" indicate something gentle or harmless, "benevolent" relates to being kind and generous, and "brittle" suggests fragility or lack of resilience. None of these terms convey the idea of someone who is quarrelsome or ill-tempered as effectively as "cantankerous" does. Therefore, it stands out as the most accurate descriptor in this context.