You don't really need TA advice for the falls: Stay in the Belmond on the Brazil side. Bird Park is a couple blocks walk from the hotel shuttle stop at the park entrance. If you want to see the big power plant, the hotel can arrange it. If you go to the Argentina side, stay in the Sheraton in the park, although it's not luxury. Beyond this, you might want a hotel car or taxi to go shopping in town if this interests you.