Chris King, who seems to know his stuff.
An IH should be cheaper to make as the tolerances on the headtube are not as tight. Aero and such is negligable. IMHO it's like other integrated parts. It works (well, sort of) so long as you don't want to change anything. I don't believe that people's problems with loosening headsets are related to cheap compression plugs and such. I don't really inderstand how an IH cann loosen the clamp above it unless the entire system is poorly machined and can slide.