We stayed in Ipanema. Easy walk to Leblon and fine shopping. We were able to walk to the Botanical Gardens (a must-see) even though it was raining. Had a superb private guide who took us out of the city to the suburbs and to a native Indian village.
Embarkation in Rio was a bit frustrating...porters demanding money (we had carry-ons only so politely declined), long lines, and a bit of confusion as to what line we were supposed to be in.
Old City (Ciudad Vieja) very quaint and very quiet (we were there on a Saturday) but in sad disrepair. We had a private walking tour which was quite interesting. The port market was very busy but we didn't spend much time there.
We had a private walking tour (7 hours) of the city with a stop for lunch on our first day (of a two night overnight) We covered a lot of ground! The second day went to an estancia on a ship excursion. Although the estancia was pretty, the food was not good and there was repetitive dancing exhibition (once would have been sufficient). The promised gaucho exhibition consisted of just one activity, trying to get a ring off a bar while riding horseback. I expected something more. Buenos Aires itself is a very interesting city with some very beautiful areas as well as some very gritty areas. Post cruise we went to Iguazu on our own (excellent trip) and then returned to stay in Buenos Aires in the Palermo Soho area for a couple of days.