“Because I really like working with them….” is an acceptable reason for selecting and maintaining a business relationship.
Assuming all other things being equal in the product or service, “likeability,” or “ease of working relationship,” in itself can be a differentiator.
A good goal is to leave any person or interaction more “energy positive” and to provide value in whatever way is appropriate to the assignment or situation; to provide a solution, path to solution, recommendation, or to help simplify to a point of clarity.
Be the person others like working with.