Answer:
I would fire Gary.
Explanation:
Even if Gary has a better sales record, he seems to be unable to keep good personal relationships, both with coworkers and clients. This in the long-run could become more problematic and lead to a decline in sales record, and also, a decline in other areas.
Brenda, on the other hand, needs to improve her sales record, but she has strong interpersonal skills that give her an advatange. It is easier to teach a person how to sell than how to be a well-mannered person, therefore, in theory, if should not be so difficult to help Brenda reach higher sales.