When a couple is selling a home which of them typically decides which real estate agent to use?

There is no "typical" answer to your question. It can depend on the dynamics of the relationship and even the Demographics. Some couples rely on the one who is better at making important decisions. Many couples have already worked out that aspect of their relationship and have a way to make those decisions together. Many others rely on that old patriarchal rule that by accident of birth the man of the house makes important decisions.