When you interview for internships, check the competitive pyramid to see whether promotions are fairly determined, whether interns would choose their program again, whether they ask questions at conferences, and whether thay are awake at conferences. Do all this discreetly, since some of the housestaff escorting you around will be asked for their opinion of you as a candidate and potential colleague. Note how many patients the interns follow, on average.
Observe how well they are supervised.