I am very familiar with Rio, and Copacabana in particular. I would not consider anything in Barra, no matter the price. The Marriott is by far a much better choice than the Sheraton, which is in an isolated and inconvenient location away from everything. I am not sure why RafKa thinks the Hilton Copa is in a seedy location. I was by there just last night, and was surprised at how that entire area (the Lido) has livened up over the last little while. But then I remember it from the days when the Meridien (now Hilton) was closed and a blight on the area. The Marriott was renovated a few years ago, and is in a very central and convenient location in Copacabana; the OP won't go wrong staying there.