Paudimar is the Brazilian sister to the Hostel Inn on the Argentinean side. While it's not as big or as fancy as its famous sister, it's also part of the HI network, and it's also a nice place to stay. They're a bit far out of town, but their spacious out-of-the-way location gives them room for an enormous garden, a set of hammocks, a nice swimming pool, and camping space. They also have a tour agency on-site, for all your booking needs.
Rooms: fairly basic beds and dorms, but nice and quiet.
People: as well as the usual hostel-to-hostel backpackers, they also attract a few of the more rugged and interesting types, since they have camping and trailer-home areas.
Staff: helpful enough, and most of them speak English.
Location: a bit of a pain-in-the-a$$ spot, to tell the truth — 12km from town, and you need to catch 2 buses to get there. However, they are fairly close to both the waterfalls, and to the int'l airport.
Food: nice buffet breakfast, and the all-you-can-eat dinner is pretty good too.
Internet: only 1 free PC — very hard to get on it! In fact, you generally need to book it on the whiteboard. They also have (total rip-off) by-the-minute PCs, and Wi-Fi for laptop owners.
Hot water: works well.