Why? A dual-hose portable is more efficient than a single-hose, but a PTAC should (in theory) be more efficient (and possibly quieter) on account of having the heat-emitting side of the cooling loop outside of the living space, which is closer to the ideal split system - though I suppose that advantage could be undermined by the unit's age and condition.

Portable ACs are generally less efficient than regular window ACs and PTAC units since the compressor is inside the room.