Most of the reviews above about Sergio's Airbnb and Sergio himself are largely accurate in my experience. Sergio's Airbnb on Rua Santa Clara is very close to and just a few minutes walking from Copacabana and Ipanema beaches and convenient for shops, restaurants, bakeries, etc. It is also just the right distance from the beach that the traffic is a bit calmer and noise levels low, especially where the room is located. The room may be a tad bit on the smaller side, but it is more than made up by the vast amount of space you have all to yourself on the terrace and penthouse of the building, with a living room separate but all to yourself on the other side of the terrace, where the wifi is good for working or you can just open all the doors and windows and enjoy the breeze on a hot day while sipping a cold beverage or a Caipirinha!
Sergio is also, as others described, an excellent host who is friendly and warm. Someone who will be there for you no matter what problem you may have; he is also thoughtful about giving you space and privacy you may need or is available to chat and share with you his knowledge and passion about Rio. Chances are that he will likely speak your language, as he speaks 6 languages well and is very well-traveled globally. All in all, I would recommend Sergio and his Airbnb.