The two aren't mutually exclusive. I take pseudophedrine whenever I have a serious sinus infection or blocked eustachian tubes because it's the only thing that promotes drainage. I also take guaifenesin for its mucosal thinning effects as a matter of course. I supplement these with nasal irrigation, DXM (if the cough is impacting my sleep), and diphenhydramine in lieu of the pseudo (again for sleep).

These drugs all have different mechanisms of action and specialties and should be used only as needed, i.e. if a symptom abates then you should stop taking whatever it is that treats it. The problem is that people are too used to combination formulations or, even worse, treating all of these drugs interchangeably. A chest cold has a different OTC treatment regimen than a sinus infection.