Great hostel! Stayed here for just one night last week and thought it was really good. From the reviews I expected it to be a trek from the station but it was SO easy to get to on the tram. The staff were really helpful, although the girl on reception was keen to speak English so I couldn't practise my German, and the reception is manned 24 hours. The atmosphere seemed friendly, although I barely spent any time socialising at the hostel. Would definitely stay here again and would recommend.
Biergarten is a nice hostel and it is super clean. The rooms are nice and the beds are comfy. The communal space is the only thing that lets it down, it is quite small and not very comfortable. Also, the communal areas are outside so it can get quite cold when the weather is bad. Nice hammocks though. It isnt really a party hostel (or at least wasnt while we were there), so you have to walk quite a way to get to the livelier places.
Books is super fun. The staff are great, especially Alex! They gave us lots of tips about things to do in Rio, how to get to places and where to go next etc. The hostel is really friendly - such a good atmosphere and a really good place to meet people. It is also nice and clean.