Do vets actually recommend brands like Hill's, Purina Pro Plan, and IAMS?

In the threads we read, these three come up most often as brands that conduct feeding trials and (in IAMS' and Purina's case) are described by commenters as meeting WSAVA-style guidelines. That said, ingredient-focused reviewers criticize them for corn, by-products, or 'filler,' so the debate between food-science credentials and ingredient quality runs throughout the discussion.