Having flown both enough last year to make HP Plat and UA 1K (I always credit my US flights to UA) I suggest that HP's execution was superior from a customer perspective. And the difference was not trivial.
Assuming that the execution I saw as a customer reflect's management competence, I imagine that US customers will either be happy to have the new management, or else the merger will swamp everybody and continue to drag US into oblivion and suck HP down with it.